Compact battery charger

A plastic battery housing has a recessed compartment with a contoured support surface which supports two AA, AAA, or AAAA batteries in the same charging position as a single C or D battery. The support surface has two concave depressions suited to support AA batteries, one on either side of a larger diameter depression suited to support either a C or a D battery. A first contact is positioned to engage the positive terminal of the C or D battery, and a second contact is positioned to engage the positive terminals of the two AA batteries. Narrow diameter concave surfaces may be formed within the AA support surfaces for alternatively supporting AAA batteries which would also engage the second contact. A sliding contact element alternatively engages the negative terminal of a single C or D battery or the two negative terminals of AA or AAA batteries.

RELATED APPLICATION 
This application claims the benefit of U.S. Provisional patent application 
Ser. No. 60/006,503, filed Nov. 9, 1995. 
FIELD OF THE INVENTION 
The present invention relates to battery charging devices in general, and 
to devices for charging standard consumer batteries in particular. 
BACKGROUND OF THE INVENTION 
In today's ever expanding world of battery powered electronic devices, the 
number and various sizes of batteries that an average household uses has 
steadily increased. Rechargeable batteries provide an attractive 
alternative to disposable batteries, due to their overall longer life and 
reduced cost per use. In addition, the interest in conserving resources 
has made the use of rechargeable batteries increasingly desirable. Due to 
the different sizes and numbers of batteries used in an average household, 
consumers often prefer battery chargers that offer numerous charging 
positions that enable simultaneous charging of all batteries necessary to 
power all the devices. Common numbers and types of rechargeable batteries 
required for particular applications are shown in Table 1. 
TABLE 1 
______________________________________ 
Number of Rechargeable Batteries Required for Different 
Applications 
Application Number of Batteries 
Size of Batteries 
______________________________________ 
Electronic Game 
8 AA 
TV Remote Control 
2 AAA 
"Boombox" 8 D 
Flashlight 2 to 4 C, D or AA 
Penlight 1 to 2 AAA 
Electric Razor 
2 AA 
Portable CD Player 
4 to 6 AA 
Toy car or Truck 
2 C 
35mm Camera 2 AA 
______________________________________ 
The marketplace has reacted to the increased consumer need to charge 
multiple batteries of various sizes by providing a large number of 
different battery chargers suitable for charging different types and 
numbers of batteries at differing rates. At the present time there are 
many different types of battery chargers available in the marketplace, 
some of which accept and charge only a few batteries of limited sizes, and 
others that accept all of the well known AAA, AA, C and D sizes. Still 
other battery chargers, like the Rayovac PS-1 and PS-2 accept and charge 
only rechargeable batteries having certain predetermined features. 
(Further details concerning predetermined features like those found in 
Rayovac PS-1 and PS-2 battery chargers are described in U.S. Pat. No. 
5,443,924 entitled "Discriminating Charger and Compatible Battery" issued 
Aug. 22, 1995 and in U.S. patent application Ser. No. 08/278,505 entitled 
"Discriminating Battery Charging System" filed Jul. 21, 1994, the 
disclosures of which are hereby incorporated by reference in their 
respective entireties.) 
For the consumer desiring an ability to charge many batteries of any size, 
eight-position chargers which accommodate C, D, AA, and AAA cells are 
available, but these chargers are relatively large and bulky in comparison 
to most two-position chargers. Due to the widely varying consumer 
preferences, no single battery charger commercially available can meet the 
particular requirements of all or even most users. Chargers will usually 
have excess charging capacity except when charging only the largest cells. 
To provide the best value to the consumer, the total cost of the battery 
charger and the rechargeable batteries should compare favorably to the 
cost of disposable batteries supplanted by the rechargeable ones. Yet the 
cost of the charger is tied to the size of the unit. A more compact 
charger would yield reduced costs in materials, packaging and shipping. 
What is needed is a single, compact battery charger that is capable of 
providing most consumer needs. 
SUMMARY OF THE INVENTION 
The battery charger of this invention has a plastic battery housing with at 
least one recessed compartment with a contoured support surface which 
supports two AA or AAA batteries in the same charging position as a single 
C or D battery. The support surface preferably has two concave depressions 
suited to support AA batteries, one on either side of a larger diameter 
depression suited to support either a C or a D battery. A center contact 
is positioned to engage the positive terminal of the C or D battery, and 
at least one side contact is positioned to engage the positive terminals 
of the two AA batteries. Narrow diameter concave surfaces may be formed 
within the AA support surfaces for alternatively supporting AAA batteries 
which may also engage the side contact. A sliding contact element 
alternatively engages the negative terminal of a single C or D battery or 
the two negative terminals of AA or AAA batteries. A preferred embodiment 
of the present invention has four compartments capable of charging either 
four D or C cells, or eight AA or AAA cells. As devices requiring a larger 
number of AA batteries are more commonly used than devices requiring more 
than four D batteries, the charger may be economically produced and 
requires far less space than a prior art device with eight charging 
positions for C, D, or AA batteries. 
It is a feature of the present invention to provide a battery charger which 
can recharge multiple small diameter batteries in the same volume occupied 
by a single larger diameter battery. 
It is also a feature of the present invention to provide a battery charger 
which is of low cost yet which meets most consumer needs for charging 
positions. 
It is another feature of the present invention to provide a battery charger 
for multiple battery dimensions which occupies minimal volume. 
It is a further feature of the present invention to provide a battery 
charger capable of simultaneously charging different size batteries.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring more particularly to FIGS. 1-7, wherein like numbers refer to 
similar parts, a battery charger 100 for repeated charging of common 
battery sizes is shown in FIG. 1. The charger has a molded plastic housing 
102 with portions which define four charging compartments 104. Each 
compartment 104 is configured to accept twice as many AAA- or AA-cell 
batteries as C- or D-cell batteries. The housing 102 is preferably fitted 
with a hinged lid 105 to prevent dust from accumulating in the 
compartments 104. Light emitting diodes 106 protrude from the housing 102 
above each compartment, to indicate when the charger is supplying current 
to a particular battery or batteries. The charger 100 is provided with 
power by means of a removable power cord 109. Common household electrical 
current powers the battery charger 100. 
Although the charger 100 may be configured to accept a greater or lesser 
number of batteries, a preferred embodiment of the invention is shown in 
FIG. 1. The compartments 104 defined in the housing have compound curved 
surfaces which accommodate different diameter battery cells, and which 
direct the cells into electrical engagement with the cathode contacts and 
anode contacts appropriate for that type of battery. The compartments are 
preferably separated by upwardly protruding dividers 107 which are 
recessed at the mid point to provide finger access openings for the 
batteries within the compartments. 
As shown in FIG. 2, each compartment 104 has a base 111 which is formed 
with parallel concave grooves or recesses which engage and support 
batteries of differing diameters. The largest diameter groove extends 
along the center of the compartment 104 and defines a first upwardly 
opening concave support surface 110. The radius of the first support 
surface 110 is approximately the radius of a D-cell battery. As shown in 
FIG. 6, a single D-cell battery 160 is received on the first support 
surface 110, and is thereby positioned centrally within the compartment 
104. As shown in FIG. 2, a center cathode contact 130 is positioned 
centrally within the compartment 104, and an opening 126 is provided in 
the cathode end wall 113 of the compartment 104 so that the positive 
terminal nubbin of a D-cell battery 160 can engage the center cathode 
contact 130 when supported on the first support surface 110. The opening 
126 defines portions of a circle 132 of approximately the diameter of the 
D-cell battery nubbin. The nubbin protrudes into the opening 126 to engage 
an upper segment 140 of the center cathode contact 130. The circular 
portions 132 of the opening 126 prevent sideward displacement of a D-cell 
battery 160 supported on the first support surface 110, and thus 
cooperates with the first support surface to retain the D-cell battery in 
position throughout an entire charging cycle. The negative terminal of the 
D-cell battery 160 engages a positionable anode contact 146, shown in FIG. 
7. The structure of the compartment thereby holds the D-cell battery 160 
for charging. 
As shown in FIG. 5, the concave first support surface 110 alternatively 
supports a single C-cell battery 162. The C-cell battery, being smaller in 
diameter than the D-cell battery 160, makes only line contact with the 
first support surface 110. As shown in FIG. 2, the opening 126 in the 
cathode end wall 113 has portions 134 which are spaced horizontally 
approximately the width of a C-cell nubbin. The horizontally spaced 
portions 134 are positioned beneath the circular portions which receive a 
D-cell nubbin. The first support surface and the horizontally spaced 
portions 134 thus define the position of a C-cell battery 162 and hold it 
in place for engagement of the nubbin with a lower segment 141 of the 
center cathode contact 130. The negative terminal of the C-cell battery 
162 also engages against the positionable anode contact 146, shown in FIG. 
7. The diameter of the circular portions 132 and the horizontally spaced 
portions 134 shown in FIG. 2 may be selected to accommodate only a 
specially formed small nubbin on a specialized battery, to thereby prevent 
the insertion of a battery for recharging which is not suited to the 
particular electronics of the charger 100. 
The first support surface 110 thus accepts and positions either a D-cell or 
a C-cell battery. Thus the charger may readily accept four D-cells, four 
C-cells, or a combination of C-cells and D-cells totaling a maximum of 
four batteries. However, the compartments are further configured to accept 
two AA-cells 164, as shown in FIG. 4 or two AAA-cells 166, as shown in 
FIG. 3, within each compartment. 
Each compartment can compactly receive two AA- or AAA-cells, as the 
diameter of the AA-cell is approximately half the diameter of the D-cell. 
The diameter of the AAA-cell is smaller still. As shown in FIG. 2, the 
base of each compartment 111 has grooved portions which define two 
upwardly opening concave second support surfaces 114, each with a radius 
for supporting and positioning a AA-cell battery. Each second support 
surface 114 extends sidewardly from the central first support surface 110, 
and faces away from the first support surface 110. 
Whereas the first support surface engages entirely beneath a battery, as 
shown in FIG. 5, each second support surface 114 engages beneath and to 
one side of an AA-cell battery 164. As shown in FIG. 4, the other side of 
the AA-cell battery 164 engages against a vertical divider 107 or a side 
wall 168 of a terminal compartment. Thus supported on both sides, the 
AA-cell battery 164 is restrained from downward and sideward displacement, 
and is positioned for engagement with a side cathode contact 131, as shown 
in FIG. 2, which has an upper segment 142 which protrudes beyond the 
cathode end wall 113. 
A circular depression 136 is formed in the cathode end wall 113 of 
approximately the diameter of the AA-cell battery to permit the battery to 
be positioned to make contact with the contact segment 142 which protrudes 
from a vertical slot 147 in the cathode end wall 113. Where batteries of a 
particular chemistry, for example Renewal.RTM. rechargeable alkaline 
manganese batteries manufactured by Rayovac Corporation of Madison, Wis., 
are employed, it is desirable to configure the charger compartment so that 
batteries for which the charger is not electrically configured will not be 
charged. As disclosed in U.S. Pat. No. 5,443,924, the disclosure of which 
is hereby incorporated by reference herein, batteries may be formed which 
lack insulation on the radial outward portions of the positive terminal. 
The illustrated embodiment of the charger 100 employs side contacts which 
engage the uninsulated top surface of a specially formed AA-cell battery. 
The nubbin of the AA-cell battery will project through a circular opening 
137 in the center of the circular depression 136, and will not 
electrically engage the cathode contact 131. The charger of this invention 
may also be configured to accept batteries of other chemistries, for 
example, nickel-cadmium, lithium ion, and nickel metal hydride 
rechargeable batteries. 
As shown in FIG. 2, a concave, upwardly facing third support surface 118 
extends sidewardly and below each second support surface 114. The third 
support surface 118, as shown in FIG. 3, has a radius approximately equal 
to the radius of a AAA-cell battery 166. The third support surface 118 
extends fully below the AAA-cell battery 166 and positions it so that the 
positive terminal will engage with the lower segment 143 of the side 
cathode contact element 131 shown in FIG. 2. As with the AA-cell battery, 
the AAA-cell battery 166 is received within a circular depression 138 
formed in the cathode end wall 113, which is recessed more than the 
AA-cell circular depression 136, and a circular opening 139 centered in 
the circular depression receives the nubbin of the AAA-cell battery. No 
electrical contact is made at the nubbin, and hence a battery of an 
inappropriate type is not at risk of being improperly charged. 
Alternatively, the upper segment 142 and the lower segment 143 may be 
formed as a single bent flange of the contact element 131. 
As shown in FIG. 2, each support surface has a respective center of radius 
120, 122, and 124. The center of radius 120 of the first support surface 
110 is located above the center of radius 122, 124 of the second and third 
support surfaces, 116 and 118. This allows two size AA cells or two size 
AAA cells to be placed within the same space occupied by one size D cell 
or one size C cell battery. In addition, the center of radius 122 of the 
second support surface 116 is located above the center of radius 124 of 
the third support surface 118, allowing a size AA cell or a size AAA cell 
battery to placed within a single space. Such a configuration minimizes 
the space required to charge different size batteries, and thereby 
decreases the size of the battery charger 100. 
As shown in FIG. 7, in a preferred embodiment a contact element 144, 
preferably sliding, is located within each compartment 104. The contact 
element has a rigid slider 145 which is movable within a rectangular 
channel 154. A flexible metal spring 149 is connected to the slider which 
exerts upward pressure on the slider to bring it into engagement with the 
underside of the base 111 of the compartment 104. A stud 170 protrudes 
upwardly from the slider and is engageable with one of several holes 172 
formed in the first support surface 110. The holes 172 are positioned to 
correspond to the desired anode contact position for the AAA-cell, the 
AA-cell, the C-cell, and the D-cell. When a battery of a particular length 
is to be charged, the upright arm 174 of the anode contact is gripped by 
the user and tilted forward, thereby disengaging the stud 170. The contact 
element 144 is then moved into the desired position and released. The 
spring 149 then engages within a hole 172 and positions the anode contact 
at the desired distance from the cathode contacts for optimal charging. 
The anode contact 146 may be provided with projecting knobs 178 on the 
upright arm to engage a C-cell battery 162 or a D-cell battery 160. A 
cross arm 176 is electrically connected to the upright arm 174, and may be 
provided with projecting knobs 178 for engaging the negative terminals of 
either AA- or AAA-cell batteries. It should be noted that the charger may 
alternatively be provided with conventional spring-type or biased contact 
elements for the anode contacts. In addition, although holes have been 
disclosed for receiving the battery nubbins, alternative conventional 
cathode contacts may be employed, such as spring-type or biased elements. 
In the process of charging secondary batteries the amount or state of 
charge on the battery being charged should be monitored. The voltage 
produced by a secondary cell is directly related to the electrochemical 
condition of the cell. Knowing the state of charge of a cell is critical 
because the amount of current or electrical charge which a cell can accept 
is dependent on the state of charge of that cell. If the cell has been 
discharged beyond a given amount it is necessary with alkaline manganese 
batteries to charge at a low rate. If the cell is not completely 
discharged than a higher charge current can be used until the battery 
reaches a state of around 70 to 80 percent charge. Completion of the 
charge must then be at a reduced rate or current. Charging the cell too 
rapidly or over-charging the cell can damage the battery, reduce the 
battery's life or even create an unsafe condition. 
Alkaline manganese batteries, in addition to having an electrochemical 
system which produces a voltage, have a relatively high internal 
resistance. This internal resistance causes a voltage drop which, in 
accord with Ohm's Law, is dependent on the current flowing through the 
cell. It is the voltage produced by the electrochemical process within the 
battery which is indicative of the state of charge of the cell. The only 
way to accurately determine cell voltage is to perform the measurement at 
zero current flow. And the measurement must be performed accurately 
because the voltage varies only a small percentage between completely 
discharged and completely charged. Thus alkaline manganese batteries are 
charged with pulse DC current chargers which have periods of zero current 
between charging pulses, see for example U.S. Pat. No. 5,422,559 which is 
incorporated herein by reference. 
The charger 20 preferably provides rectified DC pulses at twice the line 
frequency. Line frequency is 60 Hz and 120 volts in the United States, in 
some countries the line frequency may be 50 Hz and the line voltage may be 
120 or 220 volts. A preferred transformer will incorporate a winding to 
accommodate 220 voltage and the voltage supplied by the transformer will 
be sufficiently above the needed two 1/2 volts that the charging can 
function adequately on the 90 volts supplied in some rural Japanese 
regions. The battery charger circuit utilizes a transformer to step down 
and rectify the line voltage to the charging voltage which for an alkaline 
manganese cell is about 2.5 volts. The resulting pulsed DC current has 
periods of time between DC pulses where the current supplied to the cell 
is zero. During these periods of time the open circuit voltage (i.e. the 
voltage at zero current), which corresponds to the cell state of charge 
can be monitored. The charging circuit than decides whether or not to 
provide the next pulse of DC charging current to a particular cell. 
The voltage monitoring circuit also detects whether a cell is present. In 
the battery charger 20 the presence of a detectable voltage at a given 
charging station informs the charger which stations are occupied. Knowing 
which stations are occupied in combination with the cell open circuit 
voltage allows the proper amount of current to be supplied to that cell 
depending on cell type and cell state of charge. 
The total energy a battery may store is roughly proportional to the 
battery's volume. Thus smaller cells will charge more rapidly and this 
will be detected by the open circuit voltage (OCV) measuring circuit and 
over charging will thus be avoided. The charger 20 may employ a single 8 
Amp transformer which supplies 4 Amps to two charger circuits. Each of the 
charger circuits is connected to four AA or AAA stations and two D or C 
stations. In this way eight AA batteries can be charged. 
The charge indicator lights are controlled by the charger electronic 
circuitry. 
The charging circuit controls the amount of current being sent to each 
battery by varying the number of pulses which are sent or not sent to a 
given battery. Approximately 70 percent of the power supplied by the 
transformer can be used to charge batteries within the battery charger. 
Different levels of current are selectively applied to different size 
batteries. For example, the current level supplied to each battery present 
in the charger may be the same 120 pulses per second. Each pulse has a 
peak current of about 800 milliAmps and an average current during the 
pulse of about 400 milliAmps which over the 70 percent of the cycle during 
which the pulse is present results in a overall average current available 
of 280 milliAmps. The internal impedance on the battery and its current 
state of charge controls how much current a given battery receives from a 
single pulse. The open circuit voltage which is measured each cycle 
controls how often a pulse is sent. The AAA cells rapidly reach a state of 
charge where the pulses are decreased in frequency, while the length of 
time for the D cells to reach this charge level is greater. The impedance 
of AAA cells is also higher, reducing the amount of current they receive. 
The open circuit voltage is about 1.65 volts when the battery is 
sufficiently charged that the charge light goes out. However the charger 
continues to charge every battery contained within the charger at whatever 
rate the voltage detecting circuit indicates the cell can accept without 
an over-voltage condition occurring. This may be as little as a single 
pulse every few minutes. 
It is to be understood that although the illustrated charger has support 
surfaces and contacts for the charging of D-cell, C-cell, AA-cell, and 
AAA-cell batteries, the charger may also be provided with appropriately 
shaped compartments and contact elements to receive and charge size AAAA 
cells. Furthermore, although contact arrangements for recharging Rayovac 
Corporation RENEWAL brand rechargeable alkaline manganese batteries have 
been illustrated and described, alternative contact arrangements and 
charging circuitry for charging conventional nickel cadmium or other 
rechargeable chemistries may also be employed. In addition, instead of 
employing mechanical discrimination strategies for preventing the charging 
of unsuitable battery types, electronic discrimination circuits of a 
conventional nature may be employed. 
Furthermore, although separate charging circuits for the AA and AAA battery 
contacts have been disclosed, the circuits for the AA and AAA battery 
contacts may be connected in parallel. In addition a single charger may be 
provided with mechanical or electronic discrimination and appropriate 
charging electronics to allow the acceptance of two or more battery types, 
for example RENEWAL brand batteries as well as Nickel Cadmium, Nickel 
Metal Hydride, or Lithium Ion batteries. Alternatively, common charging 
circuitry could be provided. 
Although separate positions for AA and AAA batteries are disclosed, a 
single position which accommodates both AA and AAA size batteries may be 
employed, with discrimination by height or no discrimination. Furthermore, 
although radiused concave support surfaces for the batteries have been 
shown, step-type support surfaces with generally vertical side walls to 
retain the batteries may be employed. 
It is understood that the invention is not limited to the particular 
construction and arrangement of parts herein illustrated and described, 
but embraces such modified forms thereof as come within the scope of the 
following claims.