Battery charger

A battery charger determines the completion of battery charge based on a battery temperature and a temperature rise value. In determination, if the battery temperature and the battery rise temperature belong to a region in the map, which tends to occur at the beginning of a final charging period (`In` in a step S334), a low count value "1" is added to a counter (in a step S336). If they belong to a region which tends to occur at the end of the final charging period (`In` in a step S340), a high count value "3" is added to the counter (in a step S340). If the sum of the count values exceeds a set value, completion of battery charge is determined (`High` in a step S348). That is, if temperature rise is large and the temperature rise remains large even with the charging current value being lowered, then a high count value is added to the counter. If temperature rise is large but the temperature rise does not increase very much with the charging current value being lowered, then a low count value is added to the counter. Thus, the battery can be charged to a target capacity without influences of the battery residual capacity, temperature and the like.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a battery charger suited for charging a 
battery, such as a nickel metal hydride battery, which emits high heat 
while being charged. 
2. Description of the Related Art 
Presently, a chargeable battery which can be repeatedly used for the power 
supply of, for example, a power tool is used. A nickel cadmium battery is 
popular as a battery for the power tool, and a battery charger for quickly 
charging a battery by applying high current to the battery is used. 
Specifically, the battery is quickly charged in about 20 minutes and a 
power tool can be continuously used by changing a battery to a battery 
which has been charged. 
The inventor of the present invention studied improving the performance of 
a power tool by using a nickel metal hydride battery as a battery 
therefore. Although the nickel metal hydride battery can increase a 
capacity compared to a nickel cadmium battery, it generates high heat 
while being charged. If the temperature of the battery becomes high by the 
generated heat, the electrodes and separator of the cell within the 
battery deteriorate and battery life is shortened. Due to this, it is 
impossible to quickly charge the nickel metal hydride battery with high 
current as done for the nickel cadmium battery stated above. 
Further, the nickel metal hydride battery is more sensitive to overcharge 
than the nickel cadmium battery and, if overcharged, the battery life is 
shortened. Due to this, it is necessary to avoid overcharging the battery. 
To avoid overcharge, in case of equipment which does not change one 
battery to another, 100% charge can be conducted by:integrating charging 
current and discharging current, and by charging the battery based on the 
integral value. In case of charging a plurality of batteries while 
changing one battery to another for use in a power tool as stated above, 
however, it is difficult to charge them up to 100% capacity without 
causing overcharge. 
Moreover, according to the conventional technique the battery charger for 
use in a power tool has enough charging capacity to continuously charge 
about two batteries with a view to providing a power supply circuit at low 
cost. Due to this, if three or more batteries are to be continuously 
charged, charging current is considerably lowered by a protection device. 
As a result, if continuous charge is conducted, it takes a longer time to 
charge the third or the following batteries. 
Further, the inventor of the present invention contrived a method for 
detecting the completion of 100% charge from a map in which the absolute 
temperatures of a battery and temperature rise values are mapped. With 
this method, however, it sometimes occurs that the completion of 100% 
charge is determined after 100% charge is over, depending on conditions. 
In addition, it is required to more accurately detect that a battery is 
charged to a desired capacity level by the method using the map. 
To accurately charge a plurality of types of batteries by the method using 
the map, maps for the plural types of batteries are required, 
respectively, with the result that a large storage memory is required for 
control purposes. 
Even if a method for detecting full charge from the map is used, it is 
difficult to charge batteries in the same manner. This is because various 
battery packs are employed for various voltages. Namely, a high voltage 
battery pack contains a number of battery cells and heat tends to 
accumulate within the pack. Conversely, a low voltage battery pack 
contains less battery cells and heat inside tends to diverge. 
Also, since the nickel metal hydride battery has different temperature rise 
characteristics according to the residual battery capacity, it is 
difficult to charge the nickel hydride battery of varied residual 
capacities using the above-stated map. 
Furthermore, if the quantity of current is controlled by detecting battery 
temperature, it is difficult to charge the battery using the map since the 
battery temperature changes in a different manner according to 
environmental temperature. 
Although some conventional battery chargers can switch long-time charge to 
short-time charge and vice versa, the life of a battery is considerably 
shortened during short-time charge. In addition, the battery charger 
according to the conventional technique cannot accurately charge a battery 
to desired capacity. 
If a battery pack consisting of a plurality of battery cells is used a 
number of times by repeatedly charging and discharging them, the 
capacities of the respective battery cells vary and the performance of the 
battery pack deteriorates. To deal with deterioration in performance, 
auxiliary charge is often conducted after completion of ordinary charge, 
to fully charge the respective battery cells by carrying charging current 
of about 0.1 C for one to two hours. 
Also, the capacity of a nickel metal hydride battery or nickel cadmium 
battery which has been 100% charged sharply decreases to about 90% by self 
discharge which takes place right after battery charge is stopped. 
Thereafter, the battery capacity gradually decreases by self discharge. To 
deal with a sharp decrease in capacity right after the completion of 
charge, trickle charge is sometimes conducted in which current of about 
0.02 C is continuously carried after the completion of charge. 
In the auxiliary charge and trickle charge stated above, average low 
current is applied to a battery by carrying pulse current. That is to say, 
the temperature of the battery rises when charge is completed and the 
capacity of the battery increases to a maximum. At this time, even if 
quite low current is continuously carried to the battery, the battery 
cannot be efficiently charged with the current. Considering this, pulse 
charge is adopted in which slightly high current is carried in a short 
time and then intermitted for a while. 
In the battery charger according to the conventional technique, however, 
since pulse current is carried in specified cycles, decrease in battery 
temperature after the completion of charge is delayed. A state in which 
the battery temperature is high right after the completion of charge 
continues, thereby adversely influencing the battery life. Besides, while 
the battery is kept in a high temperature state, charging efficiency is 
low. To deal with this disadvantage, the temperature of the battery may be 
lowered by making the pulse current cycle longer. If the charging current 
cycle, i.e., pulse cycle is made longer to the extent that the battery can 
be quickly cooled down, self discharge takes place in the battery while 
the current is not applied to the battery. Due to this, a variation in 
battery capacity is large when a user takes out the battery from the 
battery charger. The purpose of auxiliary charge and trickle charge 
cannot, thereby, be attained. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a battery charger capable of 
continuously charging a plurality batteries in a short time. 
A still further object of this invention is to provide a battery charger 
which can 100% charge a battery without overcharge and which ensures 
stopping the battery charging. 
A still further object of this invention is to provide a battery charger 
capable of charging a battery to a target capacity. 
A still further object of this invention is to provide a battery charger 
capable of charging a battery in a short time while temperature rise is 
being suppressed, irrespective of the type of the battery. 
A still further object of this invention is to provide a battery charger 
capable of 100% charging a battery without overcharge, irrespective of the 
type of the battery. 
A still further object of this invention is to provide a battery charger 
capable of charging a battery in a short time while temperature rise is 
being suppressed, irrespective of the type of the battery. 
A still further object of this invention is to provide a battery charger 
capable of charging a battery 100% without overcharge, irrespective of the 
type of the battery. 
A still further object of this invention is to provide a battery charger 
capable of charging a plurality of types of batteries in a short time 
while temperature rise is being suppressed. 
A still further object of this invention is to provide a battery charger 
capable of 100% charging a plurality of types of batteries without 
overcharge. 
A still further object of this invention is to provide a battery charger 
capable of charging a battery in a short time while battery temperature 
rise is being suppressed, irrespective of the residual battery capacity. 
A still further object of this invention is to provide a battery charger 
capable of 100% charging a battery without overcharge, irrespectively of 
the residual battery capacity. 
A still further object of this invention is to provide a battery charger 
capable of charging a battery in a short time while temperature rise is 
being suppressed, irrespective of environmental temperature. 
A still further object of this invention is to provide a battery charger 
capable of 100% charging a battery without overcharge, irrespective of 
environmental temperature. 
A still further object of this invention is to provide a battery charger 
capable of conducting not only short-time charge, but also long-time 
charge so as not to shorten the battery life. 
A still further object of this invention is to provide a battery charger 
capable of charging a battery to a selected target capacity. 
A still further object of this invention is to provide a battery charger 
capable of efficiently conducting auxiliary charge or trickle charge. 
A battery charger according to the present invention comprising; 
a storage device storing at least two types of maps, in which an allowable 
current value, with which a battery can be charged while a temperature 
rise of the battery is being suppressed, is mapped based on a battery 
temperature value and a battery temperature rise value, in accordance with 
a temperature of the battery charger; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
battery charger temperature detecting means for detecting the temperature 
of said battery charger; 
allowable current value retrieving means for retrieving a map corresponding 
to the battery charger temperature, from the battery charger temperature 
detected by said battery charger temperature detecting means, the 
temperature detected by said temperature detecting means and the 
temperature rise value outputted from said temperature rise value 
outputting means, and for obtaining said allowable current value; and 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current value retrieving means. 
In accordance with the more preferred teaching of the present invention, 
the map used is set so as not to carry high charging current when the 
battery charger temperature is high and corresponding to said battery 
charger temperature. 
The battery charger employs a map in which an allowable current value, with 
which a battery can be charged while battery temperature rise is being 
suppressed, is mapped based on a battery temperature value and a battery 
temperature rise value, in accordance with the temperature of the battery 
charger. In this case, the map corresponding to the temperature of the 
battery charger is retrieved based on the battery temperature and the 
temperature rise value. An allowable current value, with which the battery 
can be charged while battery temperature rise is being suppressed, is 
obtained and the battery is charged with the allowable current value. That 
is, if the nickel metal hydride batteries are continuously charged, the 
temperature of the battery charger increases, which may cause a failure in 
the battery charger. By decreasing the charging current to the extent that 
generated heat does not cause a failure in the battery charger based on 
the map, it is possible to charge a plurality of batteries in a short 
time. 
A battery charger according to the present invention comprising; 
a storage device storing a map in which an allowable current value, with 
which a battery can be charged while a temperature rise of the battery is 
being suppressed, is mapped based on a battery temperature value and a 
battery temperature rise value and in which the allowable current value is 
set low if the temperature value is high and the allowable current value 
is set low if the temperature rise value is high; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
allowable current value retrieving means for retrieving the map of said 
storage device from the temperature detected by said temperature detecting 
means and the temperature rise value outputted from said temperature rise 
value outputting means, and for obtaining said allowable current value; 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current retrieving means; 
first charge completion determining means for determining completion of 
battery charge based on whether frequency is high, whereby the temperature 
detected by said temperature detecting means and the temperature rise 
value outputted from said temperature rise value outputting means belong 
to a region indicating a final charging period in the map of said storage 
device; 
second charge completion determining means for determining completion of 
battery charge if the temperature rise value outputted from said 
temperature rise value outputting means exceeds a preset temperature rise 
value; and 
charge completing means for completing the battery charge, based on 
determinations as the completion of the battery charge by said first 
charge completion determining means, and said second charge completion 
determining means. 
In the battery, the first charge completion determining means determines 
the completion of battery charge based on whether or not a temperature 
rise value is relatively large, and the frequency with which a relatively 
low allowable current value is outputted from the map, is high, i.e., 
based on whether or not temperature rise is large and the temperature rise 
remains large even if the charging current value is lowered. Due to this, 
it is possible to charge a battery 100% without overcharge, irrespective 
of the residual battery capacity, temperature and the like. 
On the other hand, if a battery which life expires is to be charged, 
temperature rise is quite large. Due to this, if the temperature rise rate 
is high, the second charge completion determining means determines that 
battery charge is completed, whereby the charge of the battery can be 
instantly stopped without continuing long-time charge. 
A battery charger according to the present invention comprising; 
a storage device storing a map in which an allowable current value, with 
which a battery can be charged while a temperature rise of the battery is 
being suppressed, is mapped based on a battery temperature value and a 
battery temperature rise value and in which the allowable current value is 
set low, if the temperature value is high and the allowable current value 
is set low if the temperature rise value is high; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
allowable current value retrieving means for retrieving the map of said 
storage device from the temperature detected by said temperature detecting 
means, and the temperature rise value outputted from said temperature rise 
value outputting means, and for obtaining said allowable current value; 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current value retrieving means; 
first charge completion determining means for determining completion of 
battery charge based on whether frequency, with which the temperature 
detected by said temperature detecting means and the temperature rise 
value outputted from said temperature rise value outputting means belong 
to a region indicating a final charging period in the map of said storage 
device, is high; 
second charge completion determining means for determining completion of 
battery charge if the temperature value outputted from said temperature 
detecting means exceeds a preset temperature value; and 
charge completing means for completing the battery charge based on 
determinations by said first charge completion determining means and said 
second charge completion determining means. 
In the battery charger, the first charge completion determining means 
determines the completion of battery charge based on whether or not a 
temperature rise value is relatively large and whether or not the 
frequency with which a relatively low allowable current is outputted from 
the map is high, i.e., based on whether temperature rise is large and the 
temperature rise remains large even if the charging current value is 
lowered Due to this, it is possible to charge the battery 100% without 
overcharge, irrespective of the residual battery capacity, temperature and 
the like. 
On the other hand, the second charge completion determining means 
determines the charge of a battery is completed whereby temperature 
increases abnormally. By doing so, it is possible to stop battery charge 
instantly without continuing charge if the battery becomes abnormal or the 
battery is in a state in which high temperature greatly deteriorates the 
battery life. 
A battery charger according to the present invention comprising; 
a storage device storing a map in which an allowable current value, with 
which a battery can be charged while a temperature rise of the battery is 
being suppressed, is mapped based on a battery temperature value and a 
battery temperature rise value and in which the allowable current value is 
set low if the temperature value is high and the allowable current value 
is set low if the temperature rise value is high; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
voltage detecting means for detecting battery voltage; 
allowable current value retrieving means for retrieving the map of said 
storage device from the temperature detected by said temperature detecting 
means and the temperature rise value outputted from said temperature rise 
value outputting means, and for obtaining said allowable current value; 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current retrieving means; 
first charge completion determining means for determining completion of 
battery charge based on whether frequency is high; whereby the temperature 
detected by said temperature detecting means and the temperature rise 
value outputted from said temperature rise value outputting means belong 
to a region indicating a final charging period in the map of said storage 
device; 
second charge completion determining means for determining completion of 
battery charge if a decrease value of the battery voltage outputted from 
said voltage detecting means exceeds a preset decrease value; and 
charge completing means for completing the battery charge based on 
determinations by said first charge completion determining means and by 
said second charge completion determining means. 
In the battery charger, the first charge completion determining means 
determines the completion of battery charge based on whether or not a 
temperature rise value is relatively high and whether or not the frequency 
with which a relatively low allowable current value is outputted from the 
map is high, i.e., based on whether or not temperature rise is large and 
the temperature rise remains high even if the charging current value is 
lowered. Due to this, it is possible to 100% charge the battery without 
overcharge, irrespective of the residual battery capacity, temperature and 
the like. 
On the other hand, if environmental temperature is low, a battery is cooled 
and the detection of the battery temperature rise value may become 
difficult. In addition, a battery which has been stocked for a long time 
may exhibit a temperature change pattern different from an ordinary 
battery. Owing to this, if it is detected that a voltage drop is a 
predetermined degree or more, the second charge completion determining 
means determines battery charge is completed, whereby it is possible to 
stop charging the battery without continuing long-time charge. 
A battery charger according to the present invention comprising; 
a storage device storing a map in which an allowable current value, with 
which a battery can be charged while a temperature rise of the battery is 
being suppressed, is mapped based on a battery temperature value and a 
battery temperature rise value and in which the allowable current value is 
set low if the temperature value is high and the allowable current value 
is set low if the temperature rise value is high; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
allowable current value retrieving means for retrieving the map of said 
storage device from the temperature detected by said temperature detecting 
means and the temperature rise value outputted from said temperature rise 
value outputting means, and for obtaining said allowable current value; 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current retrieving means; 
first charge completion determining means for determining completion of 
battery charge based on whether frequency is high; whereby the temperature 
detected by said temperature detecting means, and the temperature rise 
value outputted from said temperature rise value outputting means, belong 
to a region indicating a final charging period in the map of said storage 
device; 
second charge completion determining means for integrating charging current 
quantity for said battery, and for determining completion of battery 
charge if an integral value exceeds a preset integral value; and 
charge completing means for completing the battery charge based on 
determinations by said first charge completion determining means, and by 
said second charge completion determining means. 
In the battery charger, the first charge completion determining means 
determines the completion of battery charge based on whether or not a 
temperature rise value is relatively high and whether or not the frequency 
with which a relatively low allowable current value is outputted from the 
map, i.e., based on whether or not temperature rise is large and the 
temperature rise remains large even if the charging current value is 
lowered. Due to this, it is possible to ensure charging the battery 100% 
without charging continuously it for a long time. 
On the other hand, the first charge completion determining means sometimes 
cannot detect the completion of battery charge for various reasons. To 
deal with this, the quantity of the charging current is integrated. If the 
integral value exceeds a predetermined value, the second charge completion 
determining means determines that the battery charge is completed, thereby 
ensuring that battery charge is stopped without continuing it for a long 
time. 
A battery charger according to the present invention comprising; 
a storage device storing a map in which an allowable current value, with 
which a battery can be charged while a temperature rise of the battery is 
being suppressed, is mapped based on a battery temperature value, and a 
battery temperature rise value and in which the allowable current value is 
set low if the temperature value is high, and the allowable current value 
is set low if the temperature rise value is high; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
allowable current value retrieving means for retrieving the map of said 
storage device from the temperature detected by said temperature detecting 
means and the temperature rise value outputted from said temperature rise 
value outputting means, and for obtaining said allowable current value; 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current retrieving means; 
charge completion determining means for determining completion of battery 
charge based on whether the temperature detected by said temperature 
detecting means, and the temperature rise value outputted from said 
temperature rise value outputting means belong to a region, which tends to 
occur in a final charging period in the map of said storage device, for 
adding a low count value to a count if the temperature detected by said 
temperature detecting means, and the temperature rise value outputted from 
said temperature rise value outputting means belong to a region, which 
tends to occur at a start of the final charging period in the map, for 
adding a high count value to the count if the temperature detected by said 
temperature detecting means, and the temperature rise value outputted from 
said temperature rise value outputting means belong to a region, which 
tends to occur at an end of the final charging period in the map, and for 
determining the completion of the battery charge if a sum of count values 
exceeds a set value; and 
charge completing means for completing the battery charge based on 
determination as the completion of the battery charge, by said first 
charge completion determining means and by said second charge completion 
determining means. 
In the battery charger, the completion of battery charge is determined 
based on whether or not the battery temperature and the battery rise value 
belong to regions in the map which tend to occur in the final charging 
period. At this time, if they belong to the regions in the map which tend 
to occur at the start of the final charging period, a low count value is 
added to the counter. If they belong to the regions which tend to occur at 
the end of the charging final period, a high count value is added to the 
counter. If the sum of the counter values exceeds a predetermined value, 
it is determined that battery charge is completed. That is, if temperature 
rise is large and the temperature rise remains large even if the charging 
current value is lowered, a high count value is added to the counter. If 
temperature rise is large but the temperature rise does not increase very 
much by lowering the charging current value, then a low count value is 
added to the counter. Due to this, it is possible to 100% charge the 
battery without overcharge, irrespective of the residual battery capacity, 
temperature and the like. In particular, depending on the setting of the 
map, it is possible to freely detect the capacity value which is set at 
85%.+-.5% or 95%.+-.5% as well as 100%. 
A battery charger capable of charging a battery of a first type and a 
battery of a second type according to the present invention comprising: 
a storage device for storing a map in which an allowable current value, 
with which the battery of the first type can be charged while a 
temperature rise of the battery of the first type is being suppressed, is 
mapped based on a battery temperature and a battery temperature rise 
value; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
battery type detecting means for detecting whether a battery is the first 
type or the second type; 
allowable current value retrieving means for retrieving the map of said 
storage device from the temperature detected by said temperature detecting 
means, and the temperature rise value outputted from said temperature rise 
value outputting means, the allowable value retrieving means, retrieving 
said map and obtaining and outputting the allowable current value if the 
battery of first type is detected by said battery type detecting means, 
the allowable value retrieving means correcting at least one of the 
temperature detected by said temperature detecting means, and the 
temperature rise value outputted from said temperature rise value 
outputting means, retrieving said map, obtaining the allowable current 
value and correcting and outputting the obtained allowable current value; 
and 
charging means for charging the battery with the allowable current value 
outputted by said allowable current retrieving means. 
The battery charger employs a map in which an allowable current value with 
which a battery can be charged while battery temperature rise is being 
suppressed, is mapped based on a battery temperature value and a battery 
temperature rise value. In this case, a battery of the first type is 
charged by retrieving the map for the first battery type and obtaining an 
allowable current value. A battery of the second type is charged by 
correcting at least one of the battery temperature and the battery 
temperature rise value, retrieving the map for the first battery type, 
obtaining the allowable current value and correcting the obtained 
allowable current value. Due to this, it is possible to charge both the 
batteries of first and second types in a short time without causing 
deterioration due to temperature rise using a single map. 
A battery charger capable of charging a battery of a first type and a 
battery of a second type according to the present invention comprising: 
a storage device for storing a map in which an allowable current value, 
with which the battery of the first type can be charged while a 
temperature rise of the battery of the first type is being suppressed, is 
mapped based on a battery temperature and a battery temperature rise 
value; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
battery type detecting means for detecting whether a battery is the first 
type or the second type; 
allowable current value retrieving means for retrieving the map of said 
storage device from the temperature detected by said temperature detecting 
means and the temperature rise value outputted from said temperature rise 
value outputting means, the allowable value retrieving means retrieving 
said map and obtaining and outputting the allowable current value, if the 
battery of the first type is detected by said battery type detecting 
means, the allowable value retrieving means correcting at least one of the 
temperature detected by said temperature detecting means, and the 
temperature rise value outputted from said temperature rise value 
outputting means, retrieving said map, obtaining the allowable current 
value and correcting and outputting the obtained allowable current value; 
charging means for charging the battery with the allowable current value 
obtained by said allowable current retrieving means; 
charge completion determining means for determining completion of battery 
charge based on whether frequency, with which the temperature detected by 
said temperature detecting means, and the temperature rise value outputted 
from said temperature rise value outputting means belong to a region 
indicating a final charging period in the map of said storage means, is 
high, the charge completion determining means directly retrieving said map 
if the battery of the first type is detected by said battery type 
detecting means, the charge completion determining means retrieving said 
map after correcting at least one of the temperature detected by said 
temperature detecting means, and the temperature rise value outputted from 
said temperature rise value outputting means; and 
charge completing means for completing the battery charge based on 
determination as the completion of the battery charge by said charge 
completion determining means. 
The battery charger employs a map in which an allowable current value with 
which a battery can be charged while battery temperature rise is being 
suppressed, is mapped based on a battery temperature value and a battery 
temperature rise value. In this case, a battery of the first type is 
charged by retrieving the map for the first battery type and obtaining an 
allowable current value. A battery of the second type is charged by 
correcting at least one of the battery temperature and the battery 
temperature rise value, retrieving the map for the first battery type, 
obtaining the allowable current value and correcting the obtained 
allowable current value. Due to this, it is possible to charge both the 
batteries of first and second types in a short time without causing 
deterioration due to temperature rise using a single map. 
In particular, the determination of battery charge is determined based on 
whether or not a temperature rise value is relatively large and whether or 
not the frequency with which a relatively low current value is outputted 
from the map is high, i.e., based on whether or not temperature rise is 
large and the temperature rise remains large even if the charging current 
value is lowered. As for the battery of the first type, the completion of 
battery charge is determined by directly retrieving the map for the first 
battery type. As for the battery of the second type, the completion of 
battery charge is determined by correcting at least one of the battery 
temperature and the battery temperature rise value and retrieving the map 
for the first battery type. Due to this, it is possible to 100% charge the 
batteries of the first and second types without overcharge using a signal 
map, irrespective of the residual battery capacity, temperature and the 
like. 
In accordance with the more preferred teaching of the present invention, 
the battery of the first type is a nickel metal hydride battery and the 
battery of the second type is a nickel cadmium battery; and 
said allowable current value retrieving means obtains the allowable current 
value by correcting the temperature rise value to a positive side and 
retrieving said map, corrects the obtained allowable current value to a 
positive side and outputs the corrected allowable current value. 
In the battery charger, a map is set for a nickel metal hydride battery 
which temperature tends to rise during charge and which tends to 
deteriorate due to temperature rise. Owing to this, optimum charging 
current control can be conducted to the nickel metal hydride battery. 
In accordance with the more preferred teaching of the present invention, 
the battery of the first type is a nickel cadmium battery and the battery 
of the second type is a nickel metal hydride battery; and 
said allowable current value retrieving means obtains the allowable current 
value by correcting the temperature rise value to a negative side and 
retrieving said map, corrects the obtained allowable current value to a 
negative side and outputs the corrected allowable current value. 
In the battery charger, a map is set for a nickel cadmium battery which 
temperature tends to rise less during charge. Owing to this, optimum 
current charging control can be conducted to the nickel cadmium battery. 
A battery charger capable of charging batteries of different types, 
characterized by comprising; 
a storage device storing a map, in which an allowable current value, with 
which a battery can be charged while a temperature rise of the battery is 
being suppressed, is mapped based on a battery temperature value and a 
battery temperature rise value, for every battery type; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
battery type detecting means for detecting a battery type; 
allowable current value retrieving means for retrieving the map for the 
battery of the detected battery type of said storage device, from the 
battery type detected by said battery type detecting means, the 
temperature detected by said temperature detecting means, and the 
temperature rise value outputted from said temperature rise value 
outputting means, and for obtaining said allowable current value; and 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current value retrieving means. 
The battery charger employs a map in which an allowable current value with 
which a battery can be charged while battery temperature rise is being 
suppressed is mapped according to the type of the battery, based on 
battery temperature and a battery temperature rise value. That is, the map 
for the corresponding battery type is retrieved based on the battery 
temperature and the temperature rise value, an allowable current value, 
with which the battery can be charged while temperature rise is being 
suppressed, is obtained and the battery is charged with the allowable 
current value. Due to this, it is possible to charge the nickel hydride 
battery, which temperature tends to rise during charge, in a short time 
without causing deterioration due to temperature rise. In addition, just 
before the completion of battery charge, the temperature rise of the 
nickel metal hydride battery is large and a relatively low current value 
is used for charge, whereby it is possible to suppress "overshoot" after 
the completion of battery charge. Besides, the nickel cadmium battery, 
which temperature rise is relatively small, can be charged in a short time 
by carrying high current. 
A battery charger capable of charging batteries of different types 
according to the present invention comprising; 
a storage device storing a map, in which an allowable current value, with 
which a battery can be charged while a temperature rise of the battery is 
being suppressed is mapped based on a battery temperature value, and a 
battery temperature rise value, and in which the allowable current value 
is set low if the temperature value is high and the allowable current 
value is set low if the temperature rise value is high for every battery 
type; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
battery type detecting means for detecting a battery type; 
allowable current value retrieving means for retrieving the map for the 
battery of the detected battery type of said storage device, from the 
battery type detected by said battery type detecting means, the 
temperature detected by said temperature detecting means and the 
temperature rise value outputted from said temperature rise value 
outputting means, and for obtaining said allowable current value; 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current value retrieving means; 
charge completion determining means for determining completion of battery 
charge based on whether frequency is high; whereby the temperature 
detected by said temperature detecting means, and the temperature rise 
value outputted from said temperature rise value outputting means belong 
to a region indicating a final charging period in the map for the battery 
of the detected battery type; and 
charge completing means for completing the battery charge based on 
determination as the completion of the battery charge by said charge 
completion determining means. 
The battery charger employs a map in which an allowable current value, with 
which a battery can be charged while battery temperature rise is being 
suppressed, according to the type of the battery is mapped based on a 
battery temperature value and a battery temperature rise value. That is, a 
map according to the battery type is retrieved based on the temperature 
value and the temperature rise value, an allowable current value with 
which the battery can be charged while temperature rise is being 
suppressed is obtained, and the battery is charged with the allowable 
current value. Due to this, it is possible to charge the nickel metal 
hydride battery, which temperature tends to rise during charge, in a short 
time without causing deterioration due to temperature rise. Additionally, 
just before the completion of battery charge, the temperature rise of the 
nickel metal hydride battery is large and the battery is charged with a 
relatively low current value, whereby it is possible to suppress 
"overshoot" after the completion of battery charge. Besides, it is 
possible to charge the nickel cadmium battery, which temperature rise is 
relatively small, in a short time, by carrying high current. 
In particular, the completion of battery charge is determined based on 
whether or not a temperature rise value is relatively large and whether or 
not the frequency with which a relative low allowable current value is 
outputted from the map is high, i.e., based on whether or not temperature 
rise is large and the temperature rise remains large even if the charging 
current value is lowered, using a map corresponding to the battery type. 
Due to this, it is possible to charge the battery 100% without overcharge, 
irrespective of the battery type. 
A battery charger capable of charging batteries of different voltages 
according to the present invention comprising; 
a storage device storing a map, in which an allowable current value, with 
which a battery can be charged while a temperature rise of the battery is 
being suppressed, is mapped based on a battery temperature value and a 
battery temperature rise value; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
battery voltage detecting means for detecting a battery voltage; 
allowable current value retrieving means for retrieving the map for the 
detected battery voltage, from the battery voltage detected, by said 
battery voltage detecting means, the temperature detected by said 
temperature detecting means and the temperature rise value outputted from 
said temperature rise value outputting means, and for obtaining said 
allowable current value; and 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current value retrieving means. 
The battery charger employs a map in which an allowable current value, with 
which a battery can be charged while battery temperature rise is being 
suppressed, is mapped corresponding to voltage, based on a battery 
temperature value and a battery temperature rise value according to the 
voltage of the battery. That is, the map for the corresponding battery 
voltage is retrieved based on the battery temperature and the battery 
temperature rise value, an allowable current value, with which the battery 
can be charged while battery temperature rise is being suppressed, is 
obtained and the battery is charged with the allowable current value. In 
other words, as for the nickel metal hydride battery which temperature 
tends to rise during charge, the battery pack which contains many battery 
cells tends to accumulate heat inside. Conversely, the battery pack which 
contains less battery cells tends to diverge internal heat. Thus, it is 
difficult to charge them in the same manner. With the configuration of the 
invention, however, it is possible to charge both of them in a short time 
without causing deterioration due to temperature rise. 
A battery charger capable of charging batteries of different voltages 
according to the present invention comprising; 
a storage device storing a map, in which an allowable current value, with 
which a battery can be charged while a temperature rise of the battery is 
being suppressed, is mapped based on a battery temperature value and a 
battery temperature rise value, for every battery voltage; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
battery voltage detecting means for detecting a battery voltage; 
allowable current value retrieving means for retrieving the map for the 
detected battery voltage, from the battery voltage detected by said 
battery voltage detecting means, the temperature detected by said 
temperature detecting means and the temperature rise value outputted from 
said temperature rise value outputting means, and for obtaining said 
allowable current value; 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current value retrieving means; 
charge completion determining means for determining completion of battery 
charge based on whether frequency is high; whereby the temperature 
detected by said temperature detecting means and the temperature rise 
value outputted from said temperature rise value outputting means belong 
to a region indicating a final charging period in the map for the battery 
voltage, and 
charge completing means for completing the battery charge based on 
determination as the completion of the battery charge by said charge 
completion determining means. 
The battery charger employs a map in which an allowable current value with 
which a battery can be charged while battery temperature rise is being 
suppressed, is mapped corresponding to voltage, based on a battery 
temperature value and a battery temperature rise value. That is, the map 
corresponding to the type of battery is retrieved based on the battery 
temperature and the battery temperature rise value, an allowable current 
value, with which the battery can be charged while battery temperature 
rise is being suppressed, is obtained, and the battery is charged with the 
allowable current value. In other words, as for the nickel metal hydride 
battery which temperature tends to rise during charge, the battery pack 
which contains many battery cells tends to accumulate heat inside. 
Conversely, the battery pack which contains less battery cells tends to 
diverge internal heat. Thus, it is difficult to charge them in the same 
manner. With the present configuration, however, it is possible to charge 
both of them in a short time without causing deterioration due to 
temperature rise. 
In particular, the completion of battery charge is determined based on 
whether or not a temperature rise value is relatively large and whether or 
not the frequency with which a relatively low allowable current value is 
outputted from the map corresponding to the battery voltage is high, i.e., 
based on whether or not temperature rise is large and the temperature rise 
remains large even if charging current value is lowered, using the map 
corresponding to the battery voltage. Due to this, it is possible to 
charge the battery 100% without overcharge, irrespective of battery 
voltage. 
A battery charger for charging a current, capable of outputting a residual 
battery capacity according to the present invention by comprising; 
a storage device storing a map, in which an allowable current value, with 
which a battery can be charged while a temperature rise of the battery is 
being suppressed, is mapped based on a battery temperature value and a 
battery temperature rise value, for every residual battery capacity; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
battery capacity receiving means for receiving the residual battery 
capacity; 
allowable current value retrieving means for retrieving the map for the 
received residual battery capacity of said storage device, from the 
battery residual capacity received by said battery capacity receiving 
means, the temperature detected by said temperature detecting means and 
the temperature rise value outputted from said temperature rise value 
outputting means, and for obtaining said allowable current value; and 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current value retrieving means. 
The battery charger employs a map in which an allowable current value with 
which a battery can be charged while battery temperature rise is being 
suppressed, which is mapped based on the battery temperature value and the 
battery temperature rise value according to the residual battery capacity. 
That is, the map corresponding to the residual capacity of a battery is 
retrieved based on the battery temperature and the temperature rise value, 
an allowable current value, with which the battery can be charged while 
battery temperature rise is being suppressed, is obtained and the battery 
is charged with the allowable current value. Due to this, it is possible 
to charge in a short time the nickel metal hydride battery which 
temperature tends to rise during charge, without causing deterioration due 
to temperature rise in accordance with the residual battery capacity. 
A battery charger for charging a battery, capable of outputting a residual 
battery capacity according to the present invention comprising; 
a storage device storing a map, in which an allowable current value, with 
which a battery can be charged while a temperature rise of the battery is 
being suppressed, is mapped based on a battery temperature value and a 
battery temperature rise value and in which the allowable current value is 
set low if the temperature value is high and the allowable current value 
is set low if the temperature rise value is high, for every residual 
battery capacity; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
residual battery capacity receiving means for receiving the residual 
battery capacity; 
allowable current value retrieving means for retrieving the map for the 
residual battery capacity detected battery voltage, from the residual 
battery capacity received by said battery capacity receiving means, the 
temperature detected by said temperature detecting means, and the 
temperature rise value outputted from said temperature rise value 
outputting means, and for obtaining said allowable current value; 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current value retrieving means; 
charge completion determining means for determining completion of battery 
charge based on whether frequency is high; with which the temperature 
detected by said temperature detecting means, and the temperature rise 
value outputted from said temperature rise value outputting means, belong 
to a region indicating a final charging period in the map for the residual 
battery capacity, and 
charge completing means for completing the battery charge based on 
determination as the completion of the battery charge by said charge 
completion determining means. 
The battery charger employs a map in which an allowable current value with 
which a battery can be charged while battery temperature rise is being 
suppressed, is mapped based on the battery temperature value and the 
battery temperature rise value according to the residual battery capacity. 
That is, the map corresponding to the residual capacity of a battery is 
retrieved based on a battery temperature value and a temperature rise 
value, an allowable current value, with which the battery can be charged 
while battery temperature rise is being suppressed, is obtained and the 
battery is charged with the allowable current value. Due to this, it is 
possible to charge in a short time the nickel metal hydride battery, which 
temperature tends to rise during charge without causing deterioration due 
to temperature rise in accordance with the residual battery capacity. 
In particular, the completion of battery charge is determined based on 
whether or not a temperature rise value is relatively large and whether or 
not the frequency with which a relatively low allowable current value is 
high; which is outputted from the map corresponding to the residual 
battery capacity, i.e., based on whether or not temperature rise is large 
and the temperature rise remains large even if the charging current value 
is lowered. Due to this, it is possible to charge the battery 100% without 
overcharge according to the residual battery capacity. Besides, the 
resolution of the map for the high residual battery capacity substantially 
increases, so that detection accuracy enhances for 100% charge. So that 
detection accuracy enhances for 100% charge. 
A battery charger according to the present invention comprising; 
a storage device storing at least two types of maps, in which an allowable 
current value, with which a battery can be charged while a temperature 
rise of the battery is being suppressed, is mapped based on a battery 
temperature value and a battery temperature rise value, in accordance with 
an environmental temperature; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
environmental temperature detecting means for detecting the environmental 
temperature; 
allowable current value retrieving means for retrieving a map for the 
environmental temperature, from the environmental temperature detected by 
said environmental temperature detecting means, the temperature detected 
by said temperature detecting means and the temperature rise value 
outputted from said temperature rise value outputting means, and for 
obtaining said allowable current value; and 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current value retrieving means. 
The battery charger employs a map in which an allowable current value with 
which a battery can be charged while battery temperature rise is being 
suppressed, is mapped based on a battery temperature value and a battery 
temperature rise value according to environmental temperature. That is, a 
map is retrieved based on the battery temperature and the temperature rise 
value, an allowable current value, with which the battery can be charged 
while battery temperature rise is being suppressed, is obtained and the 
battery is charged with the allowable current value. Although the 
temperature of the nickel metal hydride battery tends to rise during 
charge, and it rises in a different manner according to the environmental 
temperature, it is possible to charge in a short time the nickel metal 
hydride battery without causing deterioration due to temperature rise, 
irrespective of the environmental temperature. 
A battery charger according to the present invention comprising; 
a storage device storing at least two types of maps, in which an allowable 
current value, with which a battery can be charged while a temperature 
rise of the battery is being suppressed, is mapped in accordance with an 
environmental temperature based on a battery temperature value, and a 
battery temperature rise value and in which the allowable current value is 
set low if the temperature value is high and the allowable current value 
is set low if the temperature rise value is high; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
environmental temperature detecting means for detecting the environmental 
temperature; 
allowable current value retrieving means for retrieving the map for the 
environmental temperature, from the environmental temperature detected by 
said environmental temperature detecting means, the temperature detected 
by said temperature detecting means, and the temperature rise value 
outputted from said temperature rise value outputting means, and for 
obtaining said allowable current value; 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current value retrieving means; 
charge completion determining means for determining completion of battery 
charge based on whether frequency, with which the temperature detected by 
said temperature detecting means, and the temperature rise value is high; 
outputted from said temperature rise value outputting means belong to a 
region indicating a final charging period in the map for the environmental 
temperature of said storage device, and 
charge completing means for completing the battery charge based on 
determination as the completion of the battery charge by said charge 
completion determining means. 
The battery charger employs a map which is mapped based on a battery 
temperature value and a battery temperature rise value according to 
environmental temperature which is an allowable current value with which a 
battery can be charged while battery temperature rise is being suppressed. 
That is, a map is retrieved based on the battery temperature and the 
temperature rise value, an allowable current value, with which the battery 
can be charged while battery temperature rise is being suppressed, is 
obtained and the battery is charged with the allowable current value. 
Although the temperature of the nickel metal hydride battery tends to rise 
during charge and it rises in a different manner according to the 
environmental temperature, it is possible to charge in a short time the 
nickel metal hydride battery without causing deterioration due to 
temperature rise, irrespective of the environmental temperature. 
In particular, the completion of battery charge is determined based on 
whether or not a temperature rise value is relatively large and whether or 
not the frequency with which a relatively low allowable current value is 
outputted from the map corresponding to the environmental temperature is 
high, i.e., based on whether or not temperature rise is large and the 
temperature rise remains large even if the charging current value is 
lowered. Due to this, it is possible to charge the battery 100% without 
overcharge, irrespective of the environmental temperature. 
A battery charger according to the present invention comprising; 
a storage device storing maps in which the allowable current value, with 
which a battery can be charged while a temperature rise of the battery is 
being suppressed, is mapped based on a battery temperature value and a 
battery temperature rise value, said maps including a first map for 
setting a relatively high allowable current value and a second map for 
setting a relatively low allowable current value; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
map selecting means for selecting one of the first map and the second map 
of said storage device; 
allowable current value retrieving means for retrieving the map selected by 
said map selecting means, from the temperature detected by said 
temperature detecting means and the temperature rise value outputted from 
said temperature rise value outputting means, and for obtaining said 
allowable current value; and 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current value retrieving means. 
The battery charger employs a plurality of maps in which an allowable 
current value with which a battery can be charged while battery 
temperature rise is being suppressed, is mapped based on a battery 
temperature value and a battery temperature rise value. That is, a 
selected map is retrieved based on the battery temperature and the 
temperature rise value, an allowable current value, with which the battery 
can be charged while the battery temperature rise is being suppressed, is 
obtained and the battery is charged with the allowable current value. In 
this case, if the first map in which the allowable current value is set 
high is selected, high charging current is carried, thereby preventing the 
nickel metal hydride battery which temperature tends to rise from 
deteriorating due to temperature rise during charge. In other words, it is 
possible to charge in a short time the nickel metal hydride battery to the 
extent that the battery life is not shortened. On the other hand, if the 
second map in which the allowable current value is set low is selected, 
low charging current is carried. By doing so, the nickel metal hydride 
battery which life tends to deteriorate due to overcharge over a long 
time, thereby making it possible to lengthen the battery life. 
A battery charger according to the present invention comprising; 
a storage device storing maps in which the allowable current value, with 
which a battery can be charged while a temperature rise of the battery is 
being suppressed, is mapped based on a battery temperature value and a 
battery temperature rise value and in which the allowable current value is 
set low if the temperature value is high and the allowable current value 
is set low if the temperature rise value is high, said maps including a 
first map in which a target current capacity is relatively high and a 
second map in which the target current capacity is relatively low; 
temperature detecting means for detecting a current battery temperature; 
temperature rise value outputting means for obtaining the temperature rise 
value from the temperature detected by said temperature detecting means; 
map selecting means for selecting one of the first map and the second map 
of said storage device; 
allowable current value retrieving means for retrieving the map selected by 
said map selecting means, from the temperature detected by said 
temperature detecting means and the temperature rise value outputted from 
said temperature rise value outputting means, and for obtaining said 
allowable current value; 
charging means for charging the battery with the allowable current value 
retrieved by said allowable current value retrieving means; 
charge completion determining means for determining completion of battery 
charge based on whether frequency, with which the temperature detected by 
said temperature detecting means and the temperature rise value is high 
outputted from said temperature rise value outputting means, belong to a 
region indicating a final charging period in the map selected by said map 
selecting means; and 
charge completing means for completing the battery charge based on 
determination as the completion of the battery charge by said charge 
completion determining means. 
The battery charger employs a plurality of maps in which an allowable 
current value with which a battery can be charged while temperature rise 
is being suppressed, is mapped based on a battery temperature value and a 
battery temperature rise value. That is, a selected map is retrieved based 
on the battery temperature and the temperature rise value, an allowable 
current value, with which the battery can be charged while the battery 
temperature rise is being suppressed, is obtained and the battery is 
charged with the allowable current value. In this case, if the first map 
in which a target charging capacity is set high is selected, the nickel 
metal hydride battery which temperature tends to rise during charge to the 
high target charging capacity in a short time to the extent that the 
battery does not deteriorate due to temperature rise. On the other hand, 
if the second map in which the target charging capacity is set low is 
selected, battery charge is stopped before full charge, whereby the life 
of the nickel metal hydride battery which life tends to deteriorate due to 
overcharge can be lengthened. 
In particular, the completion of battery charge is determined based on 
whether or not a temperature rise value is relatively high and whether or 
not the frequency with which a relatively low allowable current value is 
high which is outputted from the map, i.e., based on whether or not 
temperature rise is large and the temperature rise remains large even if 
the charging current value is lowered. Due to this, it is possible to 
charge the battery to a target charging capacity. 
A battery charger for conducting one of auxiliary charge and trickle charge 
after completing battery charge according to the present invention 
comprising: 
a storage device storing a map in which an allowable current value, with 
which a battery can be charged in a pulse-like manner while a battery 
temperature is being suppressed, and a pulse interval are mapped based on 
a battery temperature and a battery temperature decrease value; 
temperature detecting means for detecting a current battery temperature; 
temperature decrease value outputting means for obtaining the temperature 
decrease value from the temperature detected by said temperature detecting 
means; 
allowable current value retrieving means for retrieving the map of said 
storage device from the temperature detected by said temperature detecting 
means, and the temperature decrease value outputted from said temperature 
decrease value outputting means, and for obtaining said allowable current 
value and said pulse interval; and 
charging means for charging the battery with the allowable current value 
the pulse interval detected, by said allowable current value retrieving 
means. 
In accordance with the more preferred teaching of the present invention, 
the map of said storage device is set such that if the battery temperature 
is high and the temperature decrease is small, the allowable current value 
is high and the pulse interval is long, and that if the battery 
temperature is low and the temperature decrease is large, the allowable 
current value is low and the pulse interval is short. 
The battery charger according to the present invention controls a pulse 
current value and a pulse cycle so as to be able to conduct auxiliary 
charge while decreasing the battery temperature, using a map mapped based 
on a battery temperature value and a battery temperature decrease value. 
That is, if battery temperature is high and temperature decrease is small, 
then the allowable current value is increased, the pulse cycle is made 
longer and the battery temperature is quickly decreased, thereby allowing 
efficient battery charge. On the other hand, if battery temperature is low 
or temperature decrease is large, the pulse cycle is made shorter to 
thereby maintain a 100% charging state constantly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Battery chargers in the embodiments of the present invention will be 
described with reference to the accompanying drawings. 
FIG. 1 shows a battery charger 10 in the first embodiment, FIGS. 2A and 2B 
show a battery pack 50A (for a nickel metal hydride battery) and a battery 
pack 50B (for a nickel cadmium battery) charged by the battery charger 10, 
respectively, and FIG. 3 shows a battery drill 70 driven by the battery 
packs 50A or 50B. 
As shown in FIG. 2A, the battery pack 50A containing a nickel metal hydride 
battery consists of a generally cylindrical fitted part 52 and a generally 
prismatic base 56. A key-shaped key part 54 is formed on the side of the 
fitted part 52 and the first input terminal t1 connected to the positive 
electrode of the battery, the second input terminal t2a connected to the 
negative electrode thereof, and the third terminal t3 connected to a 
temperature detecting sensor consisting of a thermistor, are arranged on 
the upper portion of the fitted part 52. As shown in FIG. 2B, the battery 
pack 50B of the nickel cadmium battery has the same constitution as the 
battery pack 50A of the nickel metal hydride battery shown in FIG. 2A 
except that the position of the second input terminal t2b in FIG. 2B is 
shifted from that of the second input terminal t2a in FIG. 2A. The battery 
charger 10 can detect whether or not the installed battery pack is for a 
nickel metal hydride battery or a nickel cadmium battery from the 
difference in the position between the second input terminals t2a and t2b. 
In addition, the battery packs 50A and 50B are adapted to different 
voltages, i.e., 14.4 V, 12V and 9.6V, based on the difference in the 
number of battery cells contained therein. 
As shown in FIG. 1, the battery charger 10 charging the battery packs 50A 
or 50B is provided with a fitting hole 12 into which the fitted part 52 of 
the battery pack 50A or 50B is fitted. A key way 14 for introducing the 
key part 54 of the fitted part 52 is formed on the sidewall of the fitting 
hole 12. The fitting hole 12 is resin molded integrally with a housing 16 
for forming the battery charger 10. In this embodiment, the key part 54 is 
provided at the fitted part 52 of the battery pack 50A or 50B and the key 
way 14 is provided at the fitting hole 12 of the battery charger 10, 
thereby preventing the battery pack 50A or 50B from being installed in a 
wrong direction. The first to third output terminals, which are not shown, 
are provided at the bottom of the fitting hole 12 to contact with the 
first to third terminals t1, t2a or t2b and t3 of the battery pack 50A or 
50B, respectively. An LED lamp 18 is provided on the upper portion of the 
battery charger 10 to indicate that a battery is being charged. 
As shown in FIG. 3, the battery drill 70 is provided with a fitting hole 72 
into which the fitted part 52 of the battery pack 50A or 50B is fitted, 
and is designed to rotate a chuck 76 by a motor, which is not shown, by 
the supply power from the first input terminal t1 and the second input 
terminal t2 of the battery pack 50A or 50B. When the battery drill 70 is 
used, a plurality of battery cells in the battery pack 50A or 50B which 
are completed with charge are sequentially used so that the battery drill 
70 can continuously operate. To this end, the battery charger 10 in this 
embodiment is designed to be capable of quickly charging the battery pack 
50A or 50B in about 20 minutes. 
FIG. 4 is a circuit arrangement within the battery charger 10. In the 
circuit shown in FIG. 4, the noise of a commercial AC power supply is 
removed by an input filter 20, the AC power is rectified and smoothed by a 
rectifying and smoothing circuit 22, and switched on and off by a 
switching device 24 provided between the rectifying and smoothing circuit 
22 and a transformer 26. The transformer 26 is provided with an auxiliary 
winding 26a from which an electromotive force is inputted into an 
auxiliary power supply 46, and applied to a primary side control circuit 
48. The primary side control circuit 48 is provided for on/off controlling 
of the switching device 24. The switching device 24 controls a duty ratio 
of charging current, and the transformer 26 decreases commercial AC power 
voltage to a suitable voltage level. 
The output of the transformer 26 is rectified and smoothed by the 
rectifying and smoothing circuit 28 and then applied to the battery pack 
50A or 50B. By doing so, the battery cell (not shown) contained in the 
battery pack 50A or 50B is applied with charging current. A current 
detecting circuit 30 and a voltage detecting circuit 32 are connected 
between the rectifying and smoothing circuit 28 and the battery pack, from 
which a charging current signal and a charging voltage signal are inputted 
to a secondary side control circuit 38, respectively. A battery type 
detecting circuit 36 is provided at a position adjacent to the battery 
pack, from which a battery type signal is inputted to the secondary side 
control circuit 38. A temperature signal from a temperature detecting 
sensor 56 provided within the battery pack is inputted into the secondary 
side control circuit 38. 
A power supply from an auxiliary power supply circuit 44 is applied to the 
secondary side control circuit 38. The secondary side control circuit 38 
stores current value control maps, to be described later, obtains a 
temperature rise value from differentiating a temperature value outputted 
from the temperature detecting sensor 56, retrieves one of the maps based 
on the temperature value and the temperature rise value and obtains an 
allowable current value with which a battery can be charged while 
suppressing the battery temperature from rising. The secondary side 
control circuit 38 then determines whether or not a duty ratio is to be 
increased based on the above-stated charging current signal, and transmits 
the duty ratio to the primary side control circuit 48 through a charging 
current value switching circuit 40 and a feedback circuit 49, accordingly. 
The constitution of the maps for use in current control as stated above 
will be described with reference to FIG. 5. 
As stated above, the secondary side control circuit 38 within the battery 
charger is provided with six types of maps, i.e., a map M1 for a 14.4 V 
nickel metal hydride battery, a map M2 for a 12V nickel metal hydride 
battery, a map M3 for a 9.6 V nickel metal hydride battery, a map M4 for a 
14.4V nickel cadmium battery, a map M5 for a 12V nickel cadmium battery 
and a map M6 for a 9.6V nickel cadmium battery. 
Normally, if charging current for a battery increases, charging time 
becomes shorter and temperature rise becomes larger. Conversely, if 
charging current decreases, charging time becomes longer and temperature 
rise becomes smaller. A nickel metal hydride battery, in particular, has 
characteristics that a temperature gradient (temperature rise value) 
greatly varies with charging current and the already charged capacity. Due 
to this, in this embodiment, battery charge is conducted while changing a 
current value so as to suppress temperature rise. In other words, the 
conventional battery charger charges a battery with a fixed current value, 
whereas the battery charger in this embodiment determines the state of a 
battery based on the absolute temperature and a temperature rise value, 
and charges the battery while changing a current value as high as possible 
with which the temperature rise of the battery can be suppressed, that is, 
while changing a current value according to the state of the battery. 
In this embodiment, if battery temperature is high, relatively low charging 
current is applied to the battery. If the battery temperature is low, 
relatively high charging current is applied to the battery. Also, if 
temperature rise is large, relatively low charging current is applied to 
the battery. If temperature rise is small, relatively high charging 
current is applied to the battery. 
Each of the maps is intended to conduct variable-control for current stated 
above and to specify an optimum current value. In each map, the horizontal 
axis indicates the absolute temperature T of a battery, and the vertical 
axis indicates a change in temperature dT/dt. Namely, if battery 
temperature is high and temperature rise is large (lower right in the 
map), relatively low charging current is applied to the battery. If 
battery temperature is high and temperature rise is small (upper right in 
the map), medium charging current is applied to the battery. If battery 
temperature is low and temperature rise is large (lower left in the map), 
medium charging current is applied to the battery. If battery temperature 
is low and temperature rise is small (upper left in the map), relatively 
high charging current is applied to the battery. In short, optimum current 
values are set in the respective regions in the map so as to satisfy both 
target charging time (about 20 minutes) and a target temperature which the 
battery reaches. 
If a battery is charged with high current at low temperature (0.degree. C. 
or lower), the performance of the battery deteriorates. Due to this, it is 
desirable to set low current values in the left row of the map so as not 
to deteriorate battery performance. 
A suited region is retrieved from the absolute temperature T of the battery 
and a change in temperature dT/dt during battery charge based on the map. 
Charging current is then controlled based on a current value specified in 
the region. For instance, if battery temperature is between T3 and T4 and 
a change in battery temperature (or a temperature rise value) is between 
X1 and X2, then a current value in a region I24 is outputted. 
Furthermore, the battery charger in this embodiment detects the completion 
of battery charge based on the movement of regions in the map. That is, 
the battery charger according to the conventional technique detects the 
completion of battery charge by monitoring either temperature or voltage 
while charging current is set at a fixed level. More specifically, the 
conventional battery charger detects a temperature rise value, a change in 
voltage and decrease in voltage after the battery is fully charged, 
thereby determining that the battery is fully charged. In the battery 
charger in this embodiment, by contrast, charging current is changed as 
stated above. Due to this, the battery charger in this embodiment cannot 
detect the completion of battery charge only by monitoring a temperature 
value and a change in temperature or a voltage value and a change in 
voltage. In this embodiment, therefore, the battery charger detects the 
completion of battery charge based on the movement of the regions in the 
map. 
While a battery is being charged, the charging current value apparently 
moves at random in the regions of the map according to changes in 
temperature value and in temperature rise value. Specifically, before the 
battery is fully charged, if temperature increases or temperature rise 
increases and a relatively small charging current region is selected, that 
is, if the lower right region in the map is selected shown in FIG. 5, then 
temperature rise becomes smaller from the decrease of current and a 
charging current value corresponds to that in the upper regions on the 
map. 
However, as the battery is close to a fully charged state, a temperature 
rise value increases due to the characteristics of the nickel metal 
hydride battery. That is to say, while a lower region in the map is 
selected because of large temperature rise, and relatively low current is 
applied to the battery, temperature rise remains large. Based on this 
principle, the battery charger in this embodiment measures current in the 
predetermined cycle (e.g., several hundred seconds' cycle). If the 
charging current value continuously (such as three consecutive times) 
enters regions I31, I32, I33, I34 and I35, in which temperature rise is 
large, and to a region I25 in which temperature is high and temperature 
rise is medium as indicated in hatching in the map, then the battery 
charger determines that battery charge is completed and stops charging the 
battery. 
The battery charger in the first embodiment is provided with six types of 
maps according to types of batteries (i.e., a nickel metal hydride battery 
and a nickel cadmium battery) and battery voltages (i.e., 14.4V, 12V and 
9.6V). It is noted that, during battery charge, the temperature of a 
nickel metal hydride battery tends to increases and the temperature of a 
nickel cadmium battery tends to increase less. This makes it difficult to 
control charging current for both the nickel metal hydride battery and the 
nickel cadmium battery based on the temperature rise values using a single 
map. Also, the tendency of temperature rise differs depending on battery 
voltages (14.4V, 12V and 9.6V). In other words, the high voltage battery 
pack contains many battery cells and heat generated inside the pack tends 
to diverge less. Conversely, the low voltage battery pack contains less 
battery cells and heat diverge greatly. Therefore, it is impossible to 
control battery packs of different voltages in the same manner based on 
temperature rise. Considering this, the battery charger in the first 
embodiment prepares six types of maps M1 to M6 in accordance with (two) 
battery types and (three) battery voltages. 
The battery charge of the battery charger will be described in more detail 
with reference to the graph of FIG. 6. 
In FIG. 6, the horizontal axis indicates charging time and the vertical 
axis indicates charging current and battery temperature. FIG. 6 
illustrates temperature rise in case of charging a nickel metal hydride 
battery for one hour and that in case of quickly charging the battery for 
comparison. 
Conventionally, to avoid generating heat at the time of charging a nickel 
metal hydride battery, 1 C charge indicated by a dashed line e in FIG. 6 
is conducted, i.e., a 2 AH nickel metal hydride battery is charged for 
about one hour (65 minutes in FIG. 6) by applying 2 A charging current to 
the battery. In case of 1 C charge, battery charge starts at a temperature 
of 20.degree. C. as indicated by a dashed line f and can be completed at 
40.degree. C. It is noted that due to the characteristics of the nickel 
metal hydride battery, the quantity of temperature rise increases at a 
point, indicated by f', just before the completion of battery charge 
(after 55 minutes) and temperature rise further increases at a point, 
indicated by f", at which battery charge is completed (overshoot f0). The 
overshoot of the nickel metal hydride battery is considered to rely on the 
gradient of temperature rise at the time of completing battery charge. If 
the gradient f'-f" is slight, temperature rise caused by overshoot is 
small. Conversely, if the gradient is steep, that is, if temperature 
greatly increases at the final period of battery charge, then the degree 
of temperature rise caused by overshoot is large. 
Meanwhile, a broken line c indicates current at the time of quickly 
charging a battery (4.5 C charge) with constant high current (9 A) so as 
to complete battery charge in about 20 minutes in the battery charger, 
according to the conventional technique. A broken line d indicates change 
in the temperature of the nickel metal hydride battery at the time of 
quickly charging the battery by the conventional battery charger. As 
indicated by the broken line d, if battery charge starts at 20.degree. C., 
the temperature of the battery reaches 70.degree. C., at which the service 
life of the nickel metal hydride battery is shortened disadvantageously, 
when the battery charge is completed. Furthermore, the temperature 
abruptly rises from a point, indicated by a reference symbol d', just 
before the completion of battery charge (after 11 minutes) and continues 
rising until a point indicated by a reference symbol d" at which battery 
charge is completed. Due to this, the temperature greatly rises further 
from a point d" at which battery charge is completed (overshoot d0), 
continues rising after the completion of battery charge due to the 
overshoot d0 and exceeds 80.degree. C., thereby shortening the service 
life of the nickel metal hydride battery. In the graph of FIG. 6, the 
temperature of the battery is 20.degree. C. at the start of battery charge 
and reaches 80.degree. C. at the completion thereof, and the battery 
exhibits a temperature rise of 60.degree. C. during battery charge. Owing 
to this, if the temperature of the nickel metal hydride battery is, for 
example, 30.degree. C. at the start of battery charge, it rises by 
60.degree. C. to 90.degree. C. or higher at which the performance of the 
battery greatly deteriorates. 
A solid line a indicates a change in charging current by the battery 
charger in the first embodiment according to the present invention. A 
solid line b indicates a change in the temperature of the nickel metal 
hydride battery at the time the battery charger charges the battery. The 
battery charger 10 in this embodiment carries relatively low charging 
current if battery temperature is high and temperature rise is large, and 
carries medium charging current if battery temperature is high and 
temperature rise is small. Also, the battery charger carries medium 
charging current if battery temperature is low and temperature rise is 
large, and carries relatively high charging current if battery temperature 
is low and temperature rise is small. Thus, in order to adjust current 
based on the temperature of the nickel metal hydride battery and the 
temperature rise value thereof, battery charge starts at a temperature of 
20.degree. C. and temperature rise is suppressed to 50.degree. C. or lower 
so as not to affect the battery life as indicated by the solid line b. In 
other words, current is adjusted to a maximum allowable current value so 
that battery temperature does not exceed a target temperature and that 
charging time is short. 
As mentioned above, the battery charger 10 constantly changes charging 
current in accordance with battery temperature and temperature rise. That 
is, during an initial charging period, in which battery temperature is low 
and temperature rise is small, the battery charger 10 carries high 
current, and during a final charging period, in which battery temperature 
is high and temperature rise is large, the battery charger 10 carries 
relatively low charging current, thereby making the temperature rise value 
small just before the completion of battery charge. More specifically, 
temperature rise is small (or the gradient of temperature rise is slight) 
from a point, indicated by a reference symbol b', just before the 
completion of battery charge (after 11 minutes) until a point, indicated 
by a reference symbol b", at which battery charge is completed. Due to 
this, temperature rise after the completion of battery charge (overshoot 
b0) becomes small, so that heat generation during and after battery charge 
is suppressed to the same level (about 50.degree. C.) as temperature rise 
during 1 C charge indicated by a dashed line f. 
While 1 C charge indicated by the dashed line f is conducted, if battery 
temperature is high at the start of battery charge such as, for example, 
if battery charge starts at a battery temperature of 30.degree. C., 
temperature rises by 30.degree. C. to 60.degree. C. at the time of the 
completion of battery charge. In this embodiment, on the other hand, 
battery temperature can be suppressed to 50.degree. C. at the time of the 
completion of charge by limiting current in accordance with temperature. 
In particular, in case of a battery for use in a power tool, the battery 
capacity is fully consumed by continuously driving a motor with high 
current, and battery charge often starts in a state in which the 
temperature reaches high. The battery charger in this embodiment is 
capable of charging a high temperature nickel metal hydride battery so 
that battery temperature does not exceed a target temperature. Thus, the 
nickel metal hydride battery can be used repeatedly. 
Specific processing by the battery charger in this embodiment will be 
described based on a flow chart shown in FIG. 7 while referring to FIGS. 5 
and 6. 
When battery charge starts, the secondary side control circuit 38 (see FIG. 
4) in the battery charger adjusts charging current and determines whether 
battery charge is completed in a predetermined cycle (in this case, a 
100-second cycle for convenience; in practice a shorter cycle, i.e., a 
10-second cycle). First, the type of a battery is judged from the output 
of the battery type detection circuit 36 (in a step S12) and the voltage 
of the battery is detected (in a step S14). The voltage is detected by 
carrying charging current for a predetermined time (e.g., one minute) and 
then detecting voltage by means of the voltage detecting circuit 32. Thus, 
the voltage of even a battery which voltage falls due to, for example, 
overdischarge can be appropriately detected. A map is then selected 
according to the detected battery type and voltage (in a step S16). In 
this example, it is assumed the battery pack 50A (nickel metal hydride 
battery, 14.4V) shown in FIG. 2A is installed at the battery charger and 
the map M1 shown in FIG. 5 is selected. 
The secondary side control circuit 38 inputs the absolute temperature T of 
the nickel metal hydride battery of the battery pack 50A (in a step S18). 
The absolute temperature T inputted is thus differentiated and a change in 
battery temperature dT/dt is calculated (in a step S20). Based on the 
absolute temperature T and the change in temperature dT/dt, an optimum 
charging current value is selected from the map with reference to FIG. 5 
(in a step S22). Since the absolute temperature T falls within a range of 
T1 to T2 as indicated by a cycle &lt;1&gt; and the change in temperature dT/dt 
is X1 or less, a region I12 is selected and relatively high current for 
4.5 C charge (9 A) is applied as indicated by the solid line a of FIG. 6. 
Thereafter, the secondary side control circuit 38 determines whether the 
absolute temperature T and the change in battery temperature dT/dt enters 
regions I31, I32, I33, I34 and I35, in which temperature rise is large, 
and region I25, in which temperature is high and temperature rise is 
medium, as indicated in hatching (in a step S24). In this case, since the 
current value is not in final charging period regions (`No` in the step 
S24), process returns to a step S18 and the control of charging current is 
continued. In a cycle &lt;2&gt; after 100 more seconds, since relatively high 
current is carried in the cycle &lt;1&gt; mentioned above, the change in 
temperature dT/dt increases (X1 to X2). A region I22 is then selected and 
a medium current value (3.5 C) is selected, accordingly. Since the medium 
current value is selected in the cycle &lt;2&gt;, the change in temperature 
dT/dt becomes X1 or less. In a cycle &lt;3&gt;, a region I12 is selected and a 
relatively high charging current value is selected again. 
As stated above, if battery charge is continued while changing the current 
value in accordance with the absolute temperature T and change in 
temperature dT/dt, the change in temperature gradually increases. Then, in 
a cycle &lt;6&gt;, the change in temperature dT/dt exceeds X2 and the absolute 
temperature T and the change in temperature dT/dt enter a region I33, as 
shown in FIG. 5. In this case, the determination result of the step 24 for 
determining whether the current value falls within the above-stated final 
charging period regions (regions I31, I32, I33, I34, I35 and I25) is Yes 
then it is determined whether there is a high probability that the current 
value falls within the final charging period regions (in a step S26). 
Specifically, if the current value is in the final charging period regions 
for three consecutive cycles, then it is determined that the probability 
of entering the final charging period regions is high. Here, by narrowing 
down the current value in the cycle &lt;6&gt;, the absolute temperature T 
decreases to T2 to T3, the change in temperature dT/dt decreases to X1 to 
X2, and the absolute temperature T and the change in temperature dT/dt 
enter the region I23 in the next cycle &lt;7&gt;. Due to this, the probability 
entering the final charging period regions is determined as `Low` in the 
step S26 and battery charge is continued while changing charging current 
in a step S30. 
In the meantime, if the absolute temperature T and the change in 
temperature dT/dt enter the region I25 belonging to the final charging 
regions in a cycle &lt;13&gt;, they enter the region I35 belonging to the final 
charging regions in the next cycle &lt;14&gt;and enter the region I35 in the 
next cycle &lt;15&gt;. In this way, if the absolute temperature T and the change 
in temperature dT/dt enter the final charging period regions three 
consecutive times, the probability of entering the final charging period 
regions is determined as `High` in the step 26 and battery charge is 
completed (in a step S28), thereby finishing all of the processing steps. 
In the above-stated example, since for convenience, description is given 
with a cycle time set at 100 seconds, it is determined that the 
probability is high if the absolute temperature T and the change in 
temperature dT/dt enter the final charging period regions three 
consecutive times. In case of making a cycle time shorter in various 
manners, it is possible to determine that the probability of entering the 
final charging period regions is high. As for a 10-second cycle, for 
instance, it is determined that the probability is high if the absolute 
temperature T and the change in temperature dT/dt enter the final charging 
period regions in eight out of ten cycles. Also, it is possible to 
determine that the probability is high if the absolute temperature T and 
the change in temperature dT/dt enter the final charging period regions in 
eight out of ten cycles, or if the absolute temperature T and the change 
in temperature dT/dt enter the final charging period regions in five 
consecutive cycles. 
As stated above, the battery charger according to the conventional 
technique for charging a nickel cadmium battery detects the completion of 
battery charge by making a current value constant and monitoring at least 
one of temperature, change in temperature, voltage and change in voltage. 
The nickel metal hydride battery, however, generates high heat while being 
charged. Due to this, it is difficult to charge the nickel metal hydride 
battery quickly to 100% capacity (in about 20 minutes) without causing 
overdischarge by means of the conventional technique. The battery charger 
in this embodiment, by contrast, continuously monitors the absolute 
temperature T and the change in temperature dT/dt while narrowing down 
charging current in accordance with the battery type and battery voltage. 
It is therefore possible to charge a nickel metal hydride battery to 100% 
capacity without causing overdischarge and also, to charge a nickel 
cadmium battery in a short time. 
That is to say, the battery charger in the first embodiment employs a map, 
in which allowable current values with which a battery can be charged 
while suppressing temperature rise in accordance with the type of the 
battery are mapped based on the temperature values of the battery and the 
temperature rise values, depending on the type of the battery. 
Specifically, the map for the corresponding battery type is retrieved from 
a battery temperature and a temperature rise value, an allowable current 
value with which a battery can be charged while suppressing the 
temperature rise of the battery is obtained and the battery is charged 
with the allowable current value. This makes it possible to charge in a 
short time a nickel metal hydride battery, which temperature tends to rise 
during charge, without deterioration due to temperature rise. In addition, 
since the temperature rise of the nickel metal hydride battery is large 
and the battery is charged with a relatively low current value just before 
the completion of battery charge, "overshoot" after the completion thereof 
can be suppressed. Besides, a nickel cadmium battery, which temperature 
rise is relatively small, can be charged in a short time by applying high 
current to the battery. 
Particularly, the completion of battery charge is determined based on 
whether or not a temperature rise value is relatively high and the 
frequency with which a relatively low allowable current value is outputted 
from the map is high, i.e., the completion of battery charge is determined 
using a map according to the battery type and voltage based on whether or 
not temperature rise is large and the temperature rise continues to be 
large even if a charging current value is lowered. Thus, 100% charge is 
possible without overdischarge irrespective of the battery type and 
voltage. 
In other words, the temperature of the nickel metal hydride battery tends 
to rise while being charged and a high voltage battery pack containing 
many battery cells tends to accumulate heat inside. Conversely, a low 
voltage battery pack containing less battery cells tends to diverge 
internal heat and it is difficult to charge batteries in the same manner 
as the high voltage battery pack. That is why the battery charger in the 
first embodiment employs a map according to the battery type and voltage 
to allow every battery to be charged in a short time without deterioration 
in battery performance due to temperature rise. 
Next, description will be given to a battery charger in the second 
embodiment according to the present invention with reference to FIGS. 8 to 
10. A plurality of maps are prepared in accordance with battery types and 
battery voltages for the battery charger in the first embodiment. In the 
battery charger in the second embodiment, by contrast, a plurality of maps 
are prepared in accordance with residual battery capacities. As shown in 
FIG. 8, two types of maps, i.e., a map M11 for a residual capacity of 30% 
and a map M12 for a residual capacity of 70% are prepared. The 30% 
residual capacity map M11 is used if the battery capacity is 50% or less 
and the 70% residual capacity map M12 is used if the battery capacity 
exceeds 50%. 
FIG. 9 shows the battery charger and a batter pack 50C in the second 
embodiment. The battery pack 50C contains a nickel metal hydride 
batteries(not shown). The battery pack 50C includes a residual capacity 
integrating circuit 52 which integrates a residual battery capacity by 
integrating the charging current of the nickel hydride battery when the 
battery is installed at the battery pack 50C, and by subtracting the 
current used when the battery is installed at a power tool (see FIG. 3), 
and a communication circuit 54 which transmits the residual capacity 
obtained by the residual capacity integrating circuit 52, to the battery 
charger side. The circuit arrangement of the battery charger is the same 
as that in the first embodiment described above with reference to FIG. 4, 
which description will not,therefore, be given herein. 
Next, processing by the secondary side control circuit 38 in the battery 
charger in the second embodiment will be described with reference to FIG. 
10. 
When battery charge starts, the secondary side control circuit 38 (see FIG. 
9) in the battery charger adjusts charging current and determines whether 
the battery charge is completed in predetermined cycles. First, the 
secondary side control circuit 38 commands the communication circuit 54 of 
the battery pack 50C to transmits a residual battery capacity (in a step 
S112) and receives the residual battery capacity transmitted from the 
communication circuit 54 (in a step S114). The circuit 38 then selects a 
map shown in FIG. 8 in accordance with the received residual battery 
capacity (in a step S116). It is assumed that a residual battery capacity 
of 40% is transmitted from the battery pack 50C and that the map M11 for 
30% residual capacity shown in FIG. 5 is selected. Thereafter, the battery 
is charged based on the map M11 (in steps S118 to 130). Processing in the 
steps S118 to S130 is the same as those in the steps S18 to S30 in the 
first embodiment described above with reference to FIG. 7, which 
description will not, therefore, be given herein. 
The battery charger in the second embodiment employs an allowable current 
value with which a battery can be charged with the temperature rise of the 
battery suppressed, while making the map in which current values are 
mapped based on battery temperature values and battery temperature rise 
values, correspondent to residual battery capacities. That is to say, a 
map corresponding to the residual battery capacity is obtained retrieved 
from the battery temperature value and temperature rise value, an 
allowable current value, with which the battery can be charged with the 
temperature rise of the battery suppressed, and the battery is charged 
with the allowable current value. By doing so, it is possible to charge in 
a short time, the nickel metal hydride battery, which temperature tends to 
rise during charge, in accordance with the residual battery capacity 
without causing deterioration due to temperature rise. 
In particular, the completion of battery charge is determined based on 
whether or not a temperature rise value is relatively high, and the 
frequency with which a relatively low allowable current value is outputted 
from a map corresponding to the residual battery capacity, is high, i.e., 
based on whether or not temperature rise is large and the temperature rise 
is continued to be large even if a charging current value is lowered. 
Thus, 100% charge is possible in accordance with the residual battery 
capacity without causing overdischarge. Further, the resolution of the map 
for high residual capacity enhances substantially. Specifically, current 
values are mapped so as to correspond to a lower capacity value (30%) in 
the map M12 for 70% residual capacity and its resolution is substantially 
higher than the map M11 for 30% residual capacity, with the result the 
charging current detecting accuracy increases up to 100%. 
Next, description will be given to a battery charger in the third 
embodiment according to the present invention with reference to FIGS. 11 
to 13. A plurality of maps are prepared for the battery charger in the 
first embodiment in accordance with battery types and battery voltages. In 
the battery charger in the third embodiment, by contrast, a plurality of 
maps are prepared for the battery charger in accordance with environmental 
temperature during charge. That is, two types of map, i.e., a map M21 for 
low temperature and a map M22 for high temperature, are prepared as shown 
in FIG. 11. If environmental temperature (or outside air temperature in a 
place in which the battery charger is provided) is below 25.degree. C., 
the low temperature map M21 is used. If 25.degree. C. or higher, the high 
temperature map M22 is used. That is, in this embodiment, battery 
temperature is detected and then charging current is determined. Due to 
the environmental temperature, the battery is cooled in a different manner 
and a single map might not be able to appropriately control the quantity 
of charging current. For that reason, two types of maps, i.e., a map for 
high temperature and a map for low temperature are prepared in this 
embodiment. 
The contents of the low temperature map M21 and the high temperature map 
M22 will be described in more detail with reference to FIG. 12. 
FIG. 12A shows the content of the low temperature map M21. A region such 
as, for instance, a region I11 in the map of FIG. 11 corresponds to the 
region I11 in FIG. 12A. If environmental temperature is low and battery 
temperature is high, the battery tends to be cooled and a change in 
temperature dT/dt to be measured is small. Owing to this, in upper right 
regions in the map, in which the absolute temperature values are high and 
the temperature rise values are low, the resolution of the absolute 
temperature T is increased (i.e., the lateral length of the regions such 
as I15, I16, I25 and I26 are shortened) and the resolution of the 
temperature rise value dT/dt is increased (i.e., the vertical lengths of 
the regions such as I15, I16, I25 and I26 are shortened). In addition, the 
vertical lengths of final charging period regions in the right of the 
map(such as I45, I46, I55, I56, I65 and I66) are expanded, thereby 
allowing optimum determination as to the completion of battery charge at 
low temperature. 
FIG. 12B shows the content of the high temperature map M22. If 
environmental temperature is high and battery temperature is low, the 
battery is not cooled by the outside air. Due to this, a temperature rise 
value dT/dt to be measured becomes higher. Considering this, the 
resolution of lower left side in the map is increased (i.e., the vertical 
lengths, for instance, of regions I41, I42, I51, I52, I61 and I62 are 
shortened) and the vertical lengths of the final charging period regions 
are narrowed, so as to allow optimum determination at high temperature as 
to the completion of battery charge. 
FIG. 13 shows the battery charger in the third embodiment. The battery 
charger includes an environmental temperature detecting circuit 43 for 
detecting environmental temperature. The detected temperature is outputted 
to the secondary side control circuit 38. The remaining circuit 
arrangement of the battery charger is the same as that in the first 
embodiment described above with reference to FIG. 4, which description 
will not therefore be given herein. 
Processing by the secondary side control circuit 38 in the battery charger 
in the third embodiment will be described with reference to FIG. 14. 
When battery charge starts, the secondary side control circuit 38 (see FIG. 
13) in the battery charger adjusts charging current and determines the 
completion of battery charge in predetermined cycles. First, an 
environmental temperature is inputted (in a step S214) and a map is 
selected in accordance with the inputted environmental temperature (in a 
step S216). In this example, it is assumed that the circuit 38 detects 
that the environmental temperature is 30.degree. C. and that the map M22 
is selected in accordance with the detected temperature. Thereafter, the 
battery is charged based on the map M22 (in steps S218 to 230). Processing 
in the steps S218 to S230 is the same as those in the steps S18 to S30 in 
the first embodiment described above with reference to FIG. 7, which 
description will not therefore be given herein. 
The battery charger in the third embodiment employs an allowable current 
value while making a map with which a battery can be charged with the 
temperature rise of the battery suppressed, in which current values are 
mapped based on battery temperature values and temperature rise values, 
correspondent to environmental temperatures. Specifically, the map is 
obtained, retrieved from the battery temperature and temperature rise 
value, an allowable current value, with which the battery can be charged 
with the temperature rise of the battery suppressed, and the battery is 
charged with the allowable current value. Although the temperature of a 
nickel hydride battery tends to rise during charge and the battery 
temperature rises in a different manner according to environmental 
temperature, the battery can be charged in a short time without causing 
deterioration due to temperature rise, irrespective of the environmental 
temperature. 
In particular, the completion of battery charge is determined based on 
whether or not a temperature rise value is relatively high and the 
frequency, with which a relatively low allowable current value is 
outputted from a map in accordance with the environmental temperature, is 
high, i.e., based on whether or not temperature rise is large and it 
remains large even if a charging current value is lowered. Thus, 100% 
charge is possible without causing discharge, irrespective of the 
environmental temperature. 
Next, description will be given to a battery charger in the fourth 
embodiment according to the present invention with references to FIGS. 15 
to 20. 
In the battery charger in the third embodiment stated above, a plurality of 
maps are prepared in accordance with environmental temperatures. In the 
battery charger in the fourth embodiment, an ordinary temperature map M31 
(a trans temperature of 60.degree. C. or lower) and a high temperature map 
M32 (a trans temperature of 60.degree. C. or higher) are prepared in 
accordance with the temperatures of the battery charger as shown in FIG. 
15. In the high temperature map M32, charging current is decreased to the 
level at which generated heat does not cause a malfunction in the battery 
charger, that is, a maximum allowable current value is set. For reference, 
the battery charger according to the conventional technique has a charging 
capacity with which two batteries can continuously be charged so as to 
provide a power supply circuit at low cost. Therefore, in case of 
continuously charging three or more batteries, a protection unit operates 
to thereby extremely lower charging current in the conventional battery 
charger. As a result, if batteries are continuously charged, it takes 
quite a long time to charge the third and the following batteries. The 
battery charger in the fourth embodiment, by contrast, employs maps 
corresponding to the temperatures of the battery charger. Due to this, 
when the temperature of the battery charger rises, charging current is 
lowered to the level at which generated heat does not cause a malfunction 
in the battery charger, that is, the third and the following batteries are 
charged in a short time by carrying the maximum allowable current. 
In the battery charger in the first embodiment, nickel metal hydride 
battery maps and nickel cadmium battery maps are individually prepared. In 
the battery charger in the fourth embodiment, by contrast, both the 
ordinary temperature map M31 and high temperature map M32 are adapted for 
a nickel metal hydride battery. Using the nickel metal hydride battery 
maps, not only a nickel metal hydride battery (battery pack 50A) but also 
a nickel cadmium battery (battery pack 50B) are charged. The nickel 
cadmium battery can appropriately be charged using the nickel metal 
hydride battery maps by correcting the input and output. 
Furthermore, in the battery charger in the fourth embodiment, regions in 
the maps are weighted at the time of determining the completion of battery 
charge. Specifically, the battery chargers in the first to third 
embodiments simply add the frequencies, indicated in hatching, with which 
the absolute temperature T and the change in temperature dT/dt enter 
regions which tends to occur at the time of the completion of charge. The 
battery charger in the fourth embodiment adds "1" to a counter when the 
absolute temperature T and the change in temperature dT/dt enter regions 
I42, I43, I34, I35 and I36 which tends to occur in the initial period of 
the completion of battery charge, and adds "2" to the counter when the 
absolute temperature T and the change in temperature dT/dt enter regions 
I51, I52, I53, I44, I45, I46, I54, I55 and I56 which tends to occur in the 
medium period of the completion of charges and adds "3" to the counter 
when the absolute temperature T and the change in temperature dT/dt enter 
regions I61, I62, I63, I64, I65 and I66 which tends to occur in the final 
period of the completion of battery charge. By doing so, the battery 
charger in the fourth embodiment detects that the battery can accurately 
be charged further to target capacity. 
Moreover, in addition to the determination of the completion of battery 
charge using maps the battery charger in the fourth embodiment stops 
charging the battery based on the integral value of the absolute 
temperature of the battery, a temperature rise value, voltage drop which 
occurs at the final charging period and charging current. 
FIG. 16 shows the battery charger in the fourth embodiment. The battery 
charger includes a trans temperature detecting circuit 42 for detecting 
the temperature of a transformer 26 and the detected temperature is 
outputted to the secondary side control circuit 38. The remaining circuit 
arrangement of the battery charger is the same as that in the first 
embodiment described above with reference to FIG. 4, which description 
will not, therefore, be given herein. The reason for detecting the 
temperature of the transformer 26 is as follows. A switching device 24 and 
the like, generate heat as in case of the transformer 26. The 
semiconductor device which constitute the switching device resists heat 
relatively stronger, whereas the insulating property of the winding of the 
transformer 26 deteriorates at 100.degree. C. or higher. The transformer 
26 is most sensitive to heat among the constituent elements of the battery 
charger. 
Processing by the secondary side control circuit 38 in the battery charger 
in the fourth embodiment will be described with reference to FIGS. 17 and 
18. 
When battery charge starts, the secondary side control circuit 38 in the 
battery charger adjusts charging current and determines the completion of 
battery charge in predetermined cycles. First, a trans temperature is 
inputted (in a step S312) and it is determined whether the trans 
temperature is ordinary temperature (below 60.degree. C.) (in a step 
S314). If the inputted temperature is ordinary temperature (below 
60.degree. C.), the ordinary temperature map M31 stated above is selected 
with reference to FIG. 15 (in a step S316). If the inputted temperature is 
equal to or higher than the ordinary temperature (60.degree. C.), the high 
temperature map M32 is selected (in a step S318). In this example, it is 
assumed that a trans temperature of 55.degree. C. is detected and the 
ordinary temperature map M31 is selected accordingly. 
Thereafter, the secondary side control circuit 38 detects a battery 
temperature (in a step S320). It is determined whether or not the battery 
temperature exceeds a preset absolute temperature To (safe temperature) 
(in a step S322). If the battery temperature exceeds the preset absolute 
temperature To (`Yes` in the step S322), battery charge is completed 
instantly (in a step S370 in FIG. 18). That is, if temperature rises 
abnormally, it is determined that battery charge is completed. Thus, 
battery charge is stopped instantly in the event that the battery becomes 
abnormal. 
On the other hand, if the battery temperature does not exceed the absolute 
temperature To (`No` in the step S322), a change in battery temperature 
dT/dt is detected (calculated) from the difference between the current 
temperature and the previously detected temperature (in a step S324). It 
is then determined whether the change in battery temperature dT/dt exceeds 
a preset change in battery temperature dTc/dt (in a step S326). If the 
battery temperature exceeds the preset change in battery temperature 
dTc/dt (`Yes` in the step S326), battery charge is completed instantly (in 
a step S370). That is temperature rise is quite large, if the battery 
which life expires is to be charged. Due to this, if temperature rise is 
quite large, it is determined that the battery charge is completed 
(incapable of being charged), thereby stopping charging the battery 
instantly without continuing charge for a long time. 
If the change in battery temperature dT/dt does not exceed the preset 
change in battery temperature dTc/dt (`No` in the step S326), the type of 
the installed battery pack is determined (in a step S328). Here, if the 
battery pack 50A for a nickel metal hydride battery is detected, the 
ordinary temperature map M31 corresponding to the nickel metal hydride 
battery stated above with reference to FIG. 15 is retrieved (in a step 
S330). If the battery pack 50B for a nickel cadmium battery is detected, 
the detected change in battery temperature dT/dt is corrected or, in this 
case, increased up to 110% (in a step S332) and the map M31 corresponding 
to the nickel metal hydride battery stated above is retrieved (in a step 
S330). The reason for correcting the input is as follows. Since the nickel 
cadmium battery generates higher heat than the nickel metal hydride 
battery and can carry relatively high current, the input value is 
increased so as to be able to set a high current value using the maps for 
a nickel metal hydride battery. 
Then, to determine the completion of battery charge, it is determined 
whether the battery temperature and the change in battery temperature 
enter the final charging period regions. If they do not belong to regions 
indicating the battery final period (`Out` in steps S334, S338 and S340), 
the counter value which is the integral value for determining the 
completion of battery charge is reset at 0 (in a step S346). On the other 
hand, if the battery temperature and the change in battery temperature 
enter regions I42, I43, I34, I35 and I36, which tend to occur in the 
initial period of the completion of battery charge (final charging period 
regions (1)) (`In` in the step S334), then "1" is added to the counter (in 
a step S336). If they enter regions I51, I52, I53, I44, I45, I46, I54, I55 
and I56 which tend to occur in the medium period of the completion of 
battery charge (final charging period regions (2)) (`In` in the step 
S338), then "2" is added to the counter (in a step S342). Further, if they 
enter regions I61, I62, I63, I64, I65 and I66, which tend to occur in the 
final period of the completion of battery charge (final charging period 
regions (3)) (`In` in the step 340), then `3` is added to the counter (in 
a step S344). Then, it is determined whether the sum of the counter value 
exceeds a preset value (such as 10) (in a step S348). If they continuously 
enter the above-stated final charging period regions and the counter value 
exceeds the preset value (`High` in a step S348), the completion of 
battery charge thereby is determined to instantly stop carrying current 
(in a step S370). 
In the meantime, if the counter value does not exceed the preset value 
(`Low` in a step S348), the value for which the map is retrieved in the 
above-stated step S330 is determined as a charging current value so as to 
continue battery charge (in a step S352 shown in FIG. 18). It is then 
determined whether the installed battery is a nickel metal hydride battery 
or a nickel cadmium battery (in a step S354). If a nickel metal hydride 
battery is installed (`Ni--NH` in the step S354), then the secondary side 
control circuit 38 outputs the current value determined in the step S352 
to the primary side control circuit 38 (in a step S357). If a nickel 
cadmium battery is installed (`Ni--Cd` in the step S354), then the current 
value determined in the step S352 is corrected (i.e., increased to 110%) 
(in a step S356) and the corrected current value is outputted to the 
primary side control circuit 38 (in a step S357). The reason for 
correcting the output is as follows. Since the nickel cadmium battery 
generates lower heat than the nickel metal hydride battery and relatively 
high current can flow, the output is increased so as to be able to set a 
high current value using the nickel metal hydride battery maps. 
Thereafter, to determine the completion of battery charge based on the 
decrease in battery voltage, it is determined whether the same current 
values are continuously outputted (in a step S358). This is because 
appropriate determination cannot be made so as to determine the completion 
of battery charge based on voltage if charging current is changed (e.g., 
current is lowered from 10A to 5A). If current is changed (`No` in the 
step S358), process goes to a step 364. If same current values are 
outputted continuously (`Yes` in the step S358), a change in battery 
voltage is detected (in a step S360) and it is determined whether the 
change in battery voltage is larger than the voltage drop (-.DELTA.V) 
which occurs at the time of completion of battery charge) (in a step 
S362). If the change in battery voltage is larger than the voltage drop 
(`Yes` in the step S362), battery charge is stopped (in a step S370). If 
the change is smaller (`No` in the step S362), process goes to a step 
S364. 
The battery charger in this embodiment determines the completion of battery 
charge based on battery voltage in the steps S358 to S362. The reason is 
as follows. If environmental temperature is low, the battery is cooled and 
the detection of a battery temperature rise value might therefore become 
difficult. Also, a battery which has been stocked for a long time exhibits 
a temperature change pattern different from an ordinary battery. Due to 
this, if a voltage drop which is equal to or more than a predetermined 
value is detected, it is determined that battery charge is completed to 
thereby stop battery charge, without continuing charging the battery for a 
long time. 
The relationship between the change in temperature and voltage while the 
environmental temperature is low will be described in more detail with 
reference to FIG. 19. In FIG. 19, the horizontal axis indicates time and 
the vertical axis indicates changes in voltage, battery temperature and 
charging temperature. Here, charging current is changing from times t1 to 
t2 (`No` in the step S358), so that completion of charge is not 
determined. After the time t2, current is not changed. Therefore, 
determination as to the completion of battery charge is started from a 
time t3 (`Yes` in the step S358). As described above, if environmental 
temperature is low and the difference between the battery temperature and 
the environmental temperature is large, the battery is cooled and it 
becomes difficult to detect a temperature rise in a region indicated by a 
reference symbol F in FIG. 18. Owing to this, if the voltage drop 
(-.DELTA.V) is detected at a time t4, even in these circumstances, it is 
determined that battery charge is completed, thereby preventing occurrence 
of overcharge. 
Referring to FIG. 18, the processing by the secondary side control circuit 
38 will be described continuously. In a step S364, charging current 
integrates by charging time to thereby calculate the quantity of charging 
current(in a step S364). It is then determined whether the quantity of 
charging current exceeds the maximum allowable charging current quantity 
(in a step S366). If the charging current quantity exceeds the maximum 
allowable charging current quantity (`Yes` in the step S366), battery 
charge is instantly completed (in a step S370). If it does not exceed the 
maximum allowable charging current quantity (`No` in the step S366), 
battery charge is continued (in a step S368). Here, the battery charger in 
the fourth embodiment may not be able to accurately detect completion of 
battery charge based on the map for various reasons; however, the battery 
charger certainly stops battery charge by determining that battery charge 
is completed if the integral value exceeds a predetermined value. 
As stated above, since the battery charger in the fourth embodiment 
determines the completion of battery charge based on a weighted map, it 
can charge a battery to target capacity more accurately, which will be 
described with reference to FIG. 20 showing the results of comparing the 
determination as to completion of charge by the battery charger (without a 
weight) in the first embodiment, with that by the battery charge (with a 
weight) in the fourth embodiment. 
In FIG. 20, (A) and (B) show the battery pack for which determination as to 
completion of charge is made by the battery charger (with a weight) in the 
fourth embodiment, whereas (C) and (D) show the battery pack for which 
determination as to completion of charge is made by the battery charge 
(without a weight) in the first embodiment. In (A), the horizontal axis 
indicates the temperature of the battery pack (-5.degree. C. to 45.degree. 
C.) at the start of battery charge and the vertical axis indicates 
percentage of charging capacity to a target charging capacity (such as 3 
AH). In the test (with a weight) shown in (A), 21 battery packs were 
tested. In the test (without a weight) shown in (C), 17 various battery 
packs were tested. (B) is a bar graph showing the result of (A) and (D) is 
a bar graph showing the result of (C). In (B) and (D), the horizontal axis 
indicate percentage of charging capacity to a target charging capacity and 
the vertical axis indicates the number of battery packs. As can be seen 
from (B), if a weight is given, the battery can be charged to 90 to 95% 
capacity without overcharge. As can be seen from (D), if a weight is not 
given, some of the batteries were charged to 100% or more and the 
quantities of charging current were not uniform. 
The battery charger in the fourth embodiment adds a high count value if 
temperature rise is large and the rise remains large even if a charging 
current value is lowered, and adds a low count value if a temperature rise 
value does not increase by lowering a charging current value, even if 
temperature rise is large. Due to this, it is possible to charge batteries 
to 100% without overcharge and without influences of the residual battery 
capacity, temperature and the like. In particular, depending on the 
settings of a map, it is possible to freely detect a capacity value which 
is set at not only 100% but also at 85%.+-.5% and 95%.+-.5%. 
The battery charger in the fourth embodiment employs maps in which 
allowable current values with which a nickel metal hydride battery can be 
charged with temperature rise suppressed, which are mapped based on the 
temperature values and temperature rise values of the battery. As for the 
nickel metal hydride battery, one of the maps is retrieved, an allowable 
temperature rise value is obtained and the battery is charged. As for a 
nickel cadmium battery, a temperature rise value (or the temperature of 
the battery) is corrected, one of the maps for a nickel metal hydride 
battery is retrieved to obtain an allowable current value and the obtained 
allowable current value is corrected to thereby charge the battery. Due to 
this, it is possible to charge both a nickel metal hydride battery and a 
nickel cadmium battery in a short time by using a single map without 
causing deterioration due to temperature rise. 
The completion of battery charge is, in particular, determined based on the 
map. As for a nickel metal hydride battery, the map is directly retrieved. 
As for a nickel cadmium battery, a battery temperature rise value is 
corrected, one of the maps for a nickel metal hydride battery is retrieved 
and the completion of battery charge is determined. Thus, it is possible 
to charge both a nickel metal hydride battery and a nickel cadmium battery 
to 100% capacity without causing overcharge and without influences of the 
residual battery capacities, temperatures and the like by using a single 
map. 
In the battery charger in the embodiment stated above, maps for a nickel 
metal hydride battery which temperature tends to increase during charge 
and tends to be easily deteriorated by temperature rise are set, and 
optimum charging current control can therefore be conducted to the nickel 
metal hydride battery. It is possible to prepare maps for a nickel cadmium 
battery so as to use the map therefore. In the latter case, as for a 
nickel metal hydride battery, a detected temperature value is corrected 
(i.e., an input value at the time of retrieving the map is lowered to 
about 90%) and the output current value obtained by retrieving the map is 
corrected (i.e., the current value is lowered to about 90%). In the latter 
case, by setting maps for a nickel cadmium battery which temperature rise 
occurs less during charge, optimum charging current control is conducted 
to the nickel cadmium battery. In the battery charger in this embodiment, 
one map deals with batteries of two different characteristics. It is also 
possible that a single map deals with three or more types of batteries. 
A battery charger in the fifth embodiment according to the present 
invention will be described next with reference to FIGS. 21 to 24. In the 
battery charger in the first embodiment stated above, a plurality of maps 
are prepared in accordance with types of batteries and battery voltages. 
In the battery charger in this embodiment, a map M41 for ordinary charging 
mode and a map M42 for quick charging mode as shown in FIG. 22 are 
prepared. 
FIG. 21 shows the outline of the battery charger in the fifth embodiment. 
The battery charger is almost the same as that in the first embodiment 
described above with reference to FIG. 1 except that a switch-over switch 
19 for switch-over of the charging map is provided in the battery charger 
in the fifth embodiment. 
FIG. 23 shows the circuit arrangement of the battery charger in the fifth 
embodiment. The battery charger is almost the same as that in the first 
embodiment described above with reference to FIG. 4, except that the 
battery charger in this embodiment is configured such that a secondary 
side control circuit 38 switches one charging map to another in accordance 
with switch-over of the switch-over switch 19. 
In the battery charger in the fifth embodiment, the normal mode map M41 is 
normally selected. Now, if a normal mode is selected, a battery is charged 
while avoiding temperature rise so as to elongate the battery life, and 
battery charge is stopped when the battery is charged to 90% capacity. 
This is because the pressure inside the battery increases and the battery 
life is shortened if the battery is charged close to 100%. On the other 
hand, if an operator depresses the switch-over switch 19, the quick 
charging mode map M52 is selected. In this case, a battery is quickly 
charged while avoiding temperature rise, and battery charge is stopped 
when the battery is charged up to 100% capacity. 
Description will now be given to processing by the secondary side control 
circuit 38 in the battery charger in the fifth embodiment with reference 
to FIG. 24. 
When battery charge starts, the secondary side control circuit 38 (see FIG. 
13) in the battery charger adjusts charging current and determines the 
completion of charge in predetermined cycles. First, a selected mode is 
inputted (in a step S414) and a map corresponding to the inputted mode is 
selected (in a step S416). In this example, it is assumed that the quick 
charging mode map M42 shown in FIG. 22 is selected. Thereafter, a battery 
is charged based on the map M42 (in steps S418 to 430). Processing in the 
steps S418 to 430 is the same as those in the steps S18 to S30 in the 
first embodiment described above with reference to FIG. 7, which 
description will not therefore be given herein. 
In the battery charger in the fifth embodiment, if the quick charging mode 
map M42, in which a high target charging capacity is set, is selected, it 
is possible to charge a nickel metal hydride battery which temperature 
tends to rise during charge in a short time to the extent that the battery 
does not deteriorate due to temperature rise. On the other hand, if the 
normal mode map, in which a low target charging capacity is set, is 
selected, battery charge is stopped before a battery is fully charged, 
whereby the life of the nickel metal hydride battery which tends to be 
affected by overcharge can be elongated, and the battery can repeatedly be 
used for a long time. 
Now, description will be given to a battery charger in the sixth embodiment 
according to the present invention with reference to FIGS. 25 to 29. The 
battery chargers in the first to fifth embodiments described above charge 
batteries to a target capacity using maps. In the battery charger in the 
sixth embodiment by contrast, after battery charge is completed by the 
battery charger in one of the first to fifth embodiments, auxiliary charge 
or trickle charge is conducted by slightly carrying current using a map. 
In the battery charger according to the conventional technique, pulsed 
current is applied when auxiliary or trickle charge is conducted. That is, 
even if low current is continuously carried, a battery which has reached 
high capacity level cannot efficiently be charged. Due to this, by 
carrying pulse current, i.e., momentarily carrying high current, auxiliary 
or trickle charge is conducted with equivalent average low current. In the 
conventional battery charger, a pulse cycle for auxiliary charge is set to 
be constant. The battery charger in the sixth embodiment, by contrast, 
detects battery temperature and a change in battery temperature by 
changing a pulse cycle while changing the quantity of pulse current to be 
applied, thereby carrying constant and average current. 
In case of conducting auxiliary charge or trickle charge while charging 
current is kept constant, decrease in battery temperature is small by 
making the pulse cycle short. Conversely, decrease in temperature is large 
if the pulse cycle is made longer. In other words, it is possible to 
determine that battery temperature can be decreased by making the pulse 
cycle longer. If the pulse cycle is made longer, a quiescent period in 
which the battery is not charged becomes longer and self-discharge is 
continuously conducted in the quiescent period. As a result, the battery 
capacity is lowered at the end of the quiescent period, i.e., just before 
the next pulse charge. If the battery pack is detached during this timing, 
the capacity becomes relatively low and the purpose of the auxiliary or 
trickle charge cannot be sufficiently attained. 
Owing to this, the battery charger in the sixth embodiment determines the 
state of the battery based on the absolute temperature of the battery and 
the temperature decrease value, and charges the battery in cycles in which 
current can be carried while decreasing the battery temperature, that is, 
by changing the pulse cycle in accordance with the state of the battery. 
In this example, the pulse cycle is changed while keeping average charging 
current constant. In other words, as shown in FIG. 27, an average of 
current IA of about 0.1 C is carried in auxiliary charge and an average of 
current IA of about 0.02 C is carried in trickle charge. When battery 
temperature is high, relatively high pulse charging current I1 is carried 
in a long cycle of TOFF1. When battery temperature is low, relatively low 
pulse charging current I2 is carried in a short cycle TOFF2. If 
temperature decrease is small, relatively high pulse charging current is 
carried in a long cycle. If temperature decrease is large, relatively low 
pulse charging current is carried in a short cycle. 
A map M51 shown in FIG. 25 is provided to conduct variable-control of 
current. In the map M51, the horizontal axis indicates the absolute 
temperature T of a battery and the vertical axis indicates change in 
temperature dT/dt. An optimum pulse cycle in which current can be carried 
while decreasing temperature is specified. That is, if battery temperature 
is high and temperature decrease is small (lower right in the map), then 
relatively long cycle pulse current is carried. If battery temperature is 
high and temperature decrease is large (upper right in the map), then 
medium cycle pulse charging current is carried. If battery temperature is 
low and temperature decrease is small (lower left in the map), then medium 
cycle pulse charging current is carried. If battery temperature is low and 
temperature decrease is large (upper left in the map), then relatively 
short cycle pulse charging current is carried. 
Description will now be given to processing by a secondary control circuit 
38 in the battery charger in the sixth embodiment with reference to FIG. 
26. 
When battery charge starts, the secondary side control circuit 38 (see FIG. 
23) in the battery charger adjusts charging current and determines the 
completion of battery charge. First, the absolute temperature T of a 
battery is inputted (in a step S512). Next, the inputted absolute 
temperature T is differentiated and a change in battery temperature dT/dt 
is calculated (in a step S514). Then, the map M51 described above with 
reference to FIG. 25 is retrieved (in a step S516) and a current value 
(the peak value of pulse current) and a quiescent time (pulse cycle) are 
determined (in a step S518). The circuit 38 carries current of the 
determined value (in a step S520) and pauses by the determined pulse cycle 
(in a step S522). If the quiescent time exceeds a set time (`No` in a step 
S524), process returns to the step 512 and battery charge is continued. 
The result of a test which compared auxiliary charge (0.1 C) by the battery 
charger in the sixth embodiment to auxiliary charge (0.1 C) by the 
conventional battery charger will be described with reference to the graph 
of FIG. 28. 
In FIG. 28, the horizontal axis indicates time and the vertical axis 
indicates battery temperature and charging current. As indicated by a 
reference symbol G in FIG. 28, the battery charger in this embodiment 
changes the charging current cycle in accordance with battery temperature 
(average current of 0.1 C). The battery charger according to the 
conventional technique, by contrast, applies pulse current in constant 
cycle as indicated by a broken line H (average current of 0.1 C). The 
battery charger in this embodiment efficiently decreases battery 
temperature as indicated by a solid line E in FIG. 28, whereas battery 
temperature is difficult to decrease in the battery charger according to 
the conventional technique as indicated by a broken line F in FIG. 28. 
The battery charger in the sixth embodiment employs a map in which current 
values are mapped based on the temperatures and temperature decrease 
values of a battery, and controls the pulse current value and pulse cycle 
so as to be able to conduct auxiliary charge while decreasing the 
temperature of the battery. That is, if battery temperature is high and 
temperature decrease is small, the battery is efficiently charged by 
increasing an allowable current value, making the pulse cycle longer and 
quickly decreasing battery temperature. On the other hand, if battery 
temperature is low or temperature decrease is large, the battery is 
constantly maintained in a state of 100% charge by decreasing the 
allowable current value and making the pulse cycle shorter. In other 
words, if the pulse cycle is made longer, a quiescent time in which the 
battery is not charged becomes long and self discharge is continuously 
conducted during the quiescent time. Then, the battery capacity is 
decreased at the end of the quiescent time, i.e., just before the next 
pulse charge. If the battery pack is detached during this timing, the 
battery capacity is relatively lowered. In this embodiment, the pulse 
cycle is made short and the quantity of self discharge in the quiescent 
time is therefore decreased, whereby it is possible to constantly maintain 
the battery to high capacity. 
The battery charger in the sixth embodiment can also be applied, not only 
to trickle charge and auxiliary charge but also to a stand-by state in 
which the battery is not charged until battery temperature decreases to an 
allowable temperature, if charging the battery which temperature rises 
after being used. 
FIG. 29 is a graph showing battery temperature, battery voltage and 
charging current while a battery is being charged by a battery charger in 
the seventh embodiment according to the present invention. As stated 
above, the battery chargers in the first to fifth embodiments adjust 
charging current by switching one current value to another in stages. The 
battery charger in the seventh embodiment, by contrast, adjusts charging 
current by switching the duty ratio of the charging current. Specifically, 
the battery chargers in the first to fifth embodiments switch the current 
value to 4 C (e.g., 8 A) -3 C (6 A)-2 C (4 A)-1 C (2 A). The battery 
charger in the seventh embodiment contains the 4C capacity of current and 
adjusts current by carrying current incessantly in case of 4 C, carrying 
current in 75% of one cycle and stopping current in 25% thereof in case of 
3C, carrying current in 50% of one cycle and stopping current in 50% 
thereof in case of 2C, and carrying current in 25% of one cycle and 
stopping current in 75% of one cycle in case of 1 C. Since the battery 
charger in the seventh embodiment adjusts the quantity of current by the 
duty ratio, it has an advantage in that current adjustment can be made 
with simple and economical constitution. 
The battery chargers in the first to seventh embodiments have been 
described as different modes. However, it goes without saying that they 
can be appropriately combined. 
Although the invention has been disclosed in the context of a certain 
preferred embodiments, it will be understood that the present invention 
extends beyond the specifically disclosed embodiments to other alternative 
embodiments of the invention. Thus, it is intended that the scope of the 
invention should not be limited by the disclosed embodiments but should be 
determined by reference to the claims that follow.