Patent Publication Number: US-11646590-B2

Title: Electric tool powered by a plurality of battery packs and adapter therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. Ser. No. 15/403,344 filed on Jan. 11, 2017, which is a divisional application of U.S. Ser. No. 14/808,090, now U.S. Pat. No. 9,583,746, which is a continuation of U.S. Ser. No. 13/770,332 filed on Feb. 19, 2013, which is a continuation of U.S. Ser. No. 12/888,100 filed on Sep. 22, 2010, now U.S. Pat. No. 8,984,711, which claims priority to Japanese Patent Application No. 2010-029505 filed on Feb. 12, 2010, the contents of which are hereby incorporated by reference into the present application. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an electric power tool powered by a plurality of battery packs and an adapter therefor. 
     DESCRIPTION OF RELATED ART 
     U.S. Pat. No. 5,028,858 discloses an electric power tool that simultaneously uses two battery packs as a power source. In this electric power tool, the two battery packs are connected in series so that a high voltage is supplied to an electric motor of the electric power tool. As a result, a higher voltage output suitable for power-intensive operations can be generated, which output is higher than is possible when only one battery pack is used as the power source. 
     SUMMARY 
     When battery packs are connected in series, the battery packs can be damaged in some situations. For example, when the charge states of the two battery packs differ, one battery pack can become over-discharged and then may be charged by the other battery pack in the reverse direction (i.e. reverse charging). In this case, the over-discharged battery pack may be damaged so seriously that it is no longer useable. 
     In an attempt to avoid this problem, U.S. Pat. No. 5,028,858 disclosed the use of two light-emitting diodes for indicating the respective charge states of the two battery packs. However, even when such indicators are provided, the battery packs can still be over-discharged or become overheated unless the user can see the indicators properly and easily. In particular, when a plurality of indicators is provided, the user must diligently watch all of the indicators. If the user does not see an indicator that is indicating an abnormality, because the indicator is located in a position not readily visible to the user, the battery pack corresponding to the indicator can still be over-discharged or become overheated. 
     In one aspect of the present teachings, this problem is addressed by arranging a plurality of indicators configured to indicate at least one condition of each respective battery pack such that all of the indicators are simultaneously viewable by the electric power tool user. Therefore, the information being communicated by all of the indicators can be conveniently and reliably conveyed to the user, such that the likelihood of a battery abnormality, which is being indicated for one or more of the battery packs, being overlooked is substantially reduced. 
     In one embodiment of the present teachings, an electric power tool preferably comprises a main body supporting a tool and an electric motor housed in the main body. A plurality of first battery interfaces is provided and each battery interface is configured to removably receive or attach one first battery pack. The plurality of first battery interfaces electrically connect a plurality of attached first battery packs in series with the electric motor. A plurality of indicators is provided and each indicator is configured to indicate at least one condition of one first battery pack attached to one of the first battery interfaces. The plurality of indicators is arranged such that all of the indicators are simultaneously viewable or visible to a single tool user. 
     With such a power tool, the tool user can conveniently and reliably view or see all of the indicators simultaneously and thus can visually recognize the respective conditions of the attached battery packs simultaneously. As a result, if an abnormality is indicated by one or more of the indicators, the tool user can immediately stop the usage of the electric power tool and thereby avoid unnecessary, and possibly irreparable, damage to the battery pack(s). 
     The present teachings can be applied to any type of cordless electric power tool, including but not limited to electric power tools for processing metals, electric power tools for processing wood, electric power tools for processing stone, and electric power tools for gardening. Specific examples include, but are not limited to, electric drills, electric impact and screw drivers, electric impact wrenches, electric grinders, electric circular saws, electric reciprocating saws, electric jig saws, electric band saws, electric hammers, electric cutters, electric chain saws, electric planers, electric nailers (including electric rivet guns), electric staplers, electric shears, electric hedge trimmers, electric lawn clippers, electric lawn mowers, electric brush cutters, electric blowers (leaf blowers), electric flashlights, electric concrete vibrators and electric vacuum cleaners. 
     In one embodiment of the present teachings, it is preferred that each battery pack comprises a plurality of lithium-ion cells and the nominal voltage of the battery packs is equal to or greater than 7.0 volts, more preferably equal to or greater than 12.0 volts and even more preferably equal to or greater than 18.0 volts. Over-discharging and overheating can cause significant damage to lithium-ion cells. Consequently, the present teachings are advantageous for preventing the lithium-ion cells from over-discharging and becoming overheated, thereby lengthening the service life of the battery packs. 
     In another embodiment, an electric power tool that normally operates at a rated voltage of 36 volts is preferably driven by two battery packs, each comprising a plurality of lithium-ion cells and each having a nominal voltage of 18 volts. In such an embodiment, the electric power tool having a higher output can be operated with the readily-available lower-voltage battery packs. Thus, the higher-voltage electric power tool (e.g., a 36 volt tool) can be used even if a corresponding high-voltage battery pack (i.e. a 36 volt battery pack) is not available to the user. Such an embodiment is also advantageous, because the lower-voltage battery pack (e.g., an 18 volt battery pack) can also be used with corresponding lower-voltage power tools (e.g., an 18 volt tool), thereby providing greater flexibility and convenience to the user. 
     The nominal voltage of a typical lithium-ion cell is 3.6 volts. Therefore, a battery pack having a nominal voltage of 18 volts includes at least five lithium-ion cells connected in series. The battery pack having a nominal voltage of 18 volts may also include, for example, ten lithium-ion cells, wherein five pairs of lithium-ion cells are connected in parallel, and the five pairs of parallel-connected lithium-ion cells are connected in series, whereby a voltage of 18 volts is output. In a similar manner, a battery pack having a nominal voltage of 18 volts can also include 15 or more lithium-ion cells by using such parallel- and series-connected cells. The higher the number of lithium-ion cells, the greater the capacity of the battery pack and consequently the smaller the electric current flowing in each lithium-ion cell during discharge of the battery due to a load being driven thereby. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a group of products according to one embodiment of the present teachings; 
         FIG.  2    shows a high-voltage electric power tool that simultaneously uses two low-voltage battery packs as a power source; 
         FIG.  3    is a top view illustrating the two low-voltage battery packs detached from the main body of the high-voltage electric tool of  FIG.  2   ; 
         FIG.  4    is a bottom view illustrating the two low-voltage battery packs detached from the main body of the high-voltage electric tool of  FIG.  2   ; 
         FIG.  5    is a schematic circuit diagram illustrating an electric circuit of the high-voltage electric tool of  FIG.  2   ; 
         FIG.  6    is a modified example of the electric circuit of  FIG.  5    having a bypass circuit added thereto; 
         FIG.  7    is a modified example of the electric circuit of  FIG.  5   , in which the position of the connection to the power supply circuit for the main controller has been changed; 
         FIG.  8    is a modified example of the electric circuit of  FIG.  5   , in which the position of the connection to the power supply circuit for the main controller has been changed and the bypass circuit has been added; 
         FIG.  9    shows two low-voltage battery packs connected to the main body of a high-voltage electric tool via an adapter having a cord connecting a pack side unit with a main body side unit; 
         FIG.  10    shows the main body side unit of the adapter of  FIG.  9    in greater detail; 
         FIG.  11    shows the pack side unit of the adapter of  FIG.  9    in greater detail; 
         FIG.  12    is a schematic circuit diagram showing a representative electric circuit of the adapter of  FIGS.  9 - 11   ; 
         FIG.  13    is a modified example of the electric circuit of  FIG.  12    having a bypass circuit added thereto; 
         FIG.  14    shows two low-voltage battery packs connected to the main body of a high-voltage electric tool via an integrated or one-piece adapter; 
         FIG.  15    shows an upper portion of the integrated adapter of  FIG.  14    in greater detail; 
         FIG.  16    shows a lower portion of the integrated adapter of  FIG.  14    in greater detail; 
         FIG.  17    shows a known low-voltage electric tool using one low-voltage battery pack as a power source; 
         FIG.  18    is a bottom view corresponding to  FIG.  17    after the low-voltage battery pack has been detached from the main body of the low-voltage electric tool; 
         FIG.  19    shows the low-voltage battery pack in greater detail; 
         FIG.  20    shows a known high-voltage electric tool having one high-voltage battery pack as a power source; 
         FIG.  21    is a top view illustrating the high-voltage battery pack detached from the main body of the high-voltage electric tool, and 
         FIG.  22    is a bottom view illustrating the high-voltage battery pack detached from the main body of the high-voltage electric tool. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG.  1    shows an exemplary, non-limiting group of cordless power tool products according to one embodiment of the present teachings. As shown in  FIG.  1   , the group of products includes two types of battery packs  10 ,  30 , three types of electric power tools  50 ,  70 ,  100 , and two types of adapters  200 ,  300 . The “high-voltage” electric power tool  70  is normally intended to use a single “high-voltage” battery pack  30  as a power source. However, the adapters  200 ,  300  may serve to electrically connect a plurality of “low-voltage” battery packs  10  to a main body  72  of the electric power tool  70  so that the electric power tool  70  is supplied with the same or substantially the same voltage as the “high-voltage” battery pack  30 . 
     In the present exemplary embodiment, the first battery pack  10  has a nominal voltage of 18 volts and the second battery pack  30  has a nominal voltage of 36 volts. For the sake of convenience in the following description, the first battery pack  10  having the nominal voltage of 18 volts will also be referred to as a “low-voltage battery pack  10 ” and the second battery pack  30  having the nominal voltage of 36 volts will also be referred to as a “high-voltage battery pack  30 ”. 
     The low-voltage battery pack  10  comprises (at least) five lithium-ion cells connected in series. The high-voltage battery pack  30  comprises (at least) ten lithium-ion cells connected in series. The two types of battery packs  10 ,  30  are preferably rechargeable using a battery charger (not shown in the figures) after being used as power sources for the electric tools  50 ,  70 ,  100 . Further, the two types of battery packs  10 ,  30  are preferably so-called “slide-type” battery packs that are attached by sliding into or onto corresponding engagement portions of the electric power tools  50 ,  70 ,  100 , the adapters  200 ,  300  or the charger. Such battery packs  10 ,  30  have already been put to practical use. In particular, the low-voltage battery pack  10  with the nominal voltage of 18 volts has been widely used. However, the structure of the battery pack connection is not particularly limited and a wide variety of battery pack connection mechanisms known in the art also may be advantageously utilized with the present teachings. 
     The low-voltage battery pack  10  can incorporate, for example, ten lithium-ion cells, rather than five lithium-ion cells, as was discussed above at the end of the Summary section. In this case, the ten lithium-ion cells comprise five pairs of lithium-ion cells connected in parallel, and the five pairs of parallel-connected lithium-ion cells are connected in series to output a voltage of 18 volts. Likewise, the high-voltage battery pack  30  can incorporate, for example, twenty lithium-ion cells, rather than ten lithium-ion cells. In this case, the twenty lithium-ion cells comprise ten pairs of lithium-ion cells connected in parallel and the ten pairs of parallel-connected lithium-ion cells are connected in series to output a voltage of 36 volts. 
     In the present exemplary embodiment, the “low-voltage” electric power tool  50  is designed to operate at a nominal voltage of 18 volts and the other two “high-voltage” electric tools  70 ,  100  are designed to operate at a nominal voltage of 36 volts. For the sake of convenience in the following description, the electric tool  50  operating at the nominal voltage of 18 volts will be referred to as a “low-voltage electric (power) tool  50 ”, and the electric tools  70 ,  100  operating at the nominal voltage of 36 volts will be referred to as “high-voltage electric (power) tools  70 ,  100 ”. As will be understood, however, the terms “low-voltage” and “high-voltage” are relative terms and are merely meant to indicate that two battery packs, which normally supply currents at different voltages, and two tools, which normally operate at different voltages, are contemplated by this aspect of the present teachings. It is not necessary that the high-voltage applications are twice the voltage of the low-voltage applications or, in fact, are any particular multiple thereof. For example, in certain applications of the present teachings, two low-voltage (e.g., 18-volt) battery packs  10  may be connected in series to a higher-voltage electric power tool that normally operates at a rated voltage that is not a multiple of the low-voltage battery packs  10 , such as, e.g., 24 volts. In this case, voltage step-down circuitry is preferably provided either in the tool or in an adapter  200 ,  300  that connects the battery packs  10  to the tool. 
     As shown in  FIG.  17    and  FIG.  18   , the low-voltage electric tool  50  is designed to normally use one low-voltage battery pack  10  as its sole power source. This low-voltage electric tool  50  is for example an electric impact driver and drives a tool chuck  54  in response to the operation of a main switch  58 . A driver set, which is a tool, can be mounted on the tool chuck  54 . Such a low-voltage electric tool  50  has already been put to practical use and has been widely sold together with the low-voltage battery pack  10  having the nominal voltage of 18 volts. 
     The main body  52  of the low-voltage electric tool  50  includes one battery interface (battery pack receptacle)  60 . The battery interface  60  is configured to removably receive or attach the low-voltage battery pack  10 , and the low-voltage battery pack  10  can be slidably received or attached therein. The battery interface  60  has a pair of rails  62 , a positive electrode input terminal  64   a , a negative electrode input terminal  64   b , and a latch receiving hole  68 . A battery controller input/output terminal is also preferably provided, but is not shown in  FIG.  18   . 
     As shown in  FIG.  19   , the low-voltage battery pack  10  includes a connector  20  that can be slidingly inserted into the battery interface  60 . The connector  20  includes a pair of rails  22 , a positive electrode output terminal  24   a , a negative electrode output terminal  24   b , and an autostop terminal  26 . When the low-voltage battery pack  10  is slidably attached to the battery interface  60 , the positive electrode output terminal  24   a  of the low-voltage battery pack  10  is electrically connected to the positive electrode input terminal  64   a  of the main body  52 , and the negative electrode output terminal  24   b  of the low-voltage battery pack  10  is electrically connected to the negative electrode input terminal  64   b  of the main body  52 . In addition, the autostop terminal  26  is connected to the battery controller input/output terminal. As a result of this sliding connection, the low-voltage battery pack  10  is also physically connected to the main body  52  of the low-voltage electric tool  50  and the battery cells  16  (see e.g.,  FIG.  5   ) are electrically connected with the internal circuitry of the tool  50 . Further, the low-voltage battery pack  10  has a latch member  12  that engages with the latch receiving hole  68  of the battery interface  60  and detachably affixes the low-voltage battery pack  10  to the battery interface  60 . The latch member  12  can be released from the latch receiving hole  68  by operating a latch release button  14 . 
     The two types of high-voltage electric tools  70 ,  100  will be explained below. The first high-voltage electric tool  70  is designed to be normally operated using one high-voltage battery pack  30  as the sole power source, as will now be explained with reference to  FIGS.  20 ,  21 , and  22   . The high-voltage electric tool  70  may be, e.g., an electric blower that includes a blower fan disposed in the main body  72  that is rotatably driven in response to the operation of a main switch  78 . The electric blower  70  is an electric power tool normally used for gardening and cleaning-up purposes by propelling air from a tip  73   a  of a nozzle  73  to move debris, such as dead leaves. The high-voltage electric tool  70  operating at a nominal voltage of 36 volts has already been put to practical use together with the high-voltage battery pack  30  that outputs a nominal voltage of 36 volts. 
     Referring to  FIG.  22   , the main body (device housing)  72  of the high-voltage electric tool  70  has one battery interface (battery pack receptacle)  80 . The battery interface  80  is configured to removably attach to the high-voltage battery pack  30 , and the high-voltage battery pack  30  can be slidably received therein. The battery interface  80  includes a pair of rails  82 , a positive electrode input terminal  84   a , a negative electrode input terminal  84   b , a battery controller input/output terminal  86  and a latch receiving hole  88 . 
     The high-voltage battery pack  30  includes a connector  40  that can be slidingly inserted into the battery interface  80 , as shown in  FIG.  21   . The connector  40  includes a pair of rails  42 , a positive electrode output terminal  44   a , a negative electrode output terminal  44   b , and an autostop terminal  46 . When the high-voltage battery pack  30  is attached to the battery interface  80 , the positive electrode output terminal  44   a  of the high-voltage battery pack  30  is connected to the positive electrode input terminal  84   a  of the battery interface  80 , and the negative electrode output terminal  44   b  of the high-voltage battery pack  30  is connected to the negative electrode input terminal  84   b  of the battery interface  80 . Further, the autostop terminal  46 , which is electrically connected to a controller of the battery pack  30  as will be discussed further below, is connected to the battery controller input/output terminal  86 . As a result, the high-voltage battery pack  30  is electrically connected to the circuitry inside the main body  72  of the high-voltage electric tool  70 . Further, the high-voltage battery pack  30  has a latch member  32  that engages with the latch receiving hole  88  of the battery interface  80  and detachable affixes the high-voltage battery pack  30  to the battery interface  80 . The latch member  32  can be released from the latch receiving hole  88  by operating a latch release button  34 . 
     The connectors  20 ,  40  of the low-voltage battery pack  10  and the high-voltage battery pack  30  may have basically the same or similar structures. However, the sizes of the connectors  20 ,  40  may differ, e.g., the spacing between the rails  22 ,  42  may differ. In this case, the low-voltage battery pack  10  cannot be attached to the battery interface  80  of the high-voltage electric tool  70 , and the high-voltage battery pack  30  cannot be attached to the battery interface  60  of the low-voltage electric tool  50 . In other words, due to the size differences in the connectors  20 ,  40 , the battery interface  80  is a dedicated interface for the high-voltage battery pack  30 , and the battery interface  60  is a dedicated interface for the low-voltage battery pack  10 . Further, in another embodiment, the interfaces  60 ,  80  may be dedicated, in addition or in the alternative, based upon differences in the shapes of the connectors  20 ,  40 . 
     Referring now to  FIGS.  2 - 4   , the second high-voltage electric tool  100  is designed to be normally operated, on the other hand, by simultaneously using two low-voltage battery packs  10  as its power source. The high-voltage electric tool  100  also may be an electric blower having a blower fan rotatably supported in a main body  102  that is driven in response to the operation of a main switch  108 . The electric blower  100  is basically identical to the above-described electric blower  70  in terms of functions and applications thereof. 
     In order to utilize current simultaneously supplied from two battery packs  10 , the main body  102  of the high-voltage electric tool  100  includes two battery interfaces (two battery pack receptacles)  130 . Each battery interface  130  is configured to removably and, e.g., slidably, receive or attach one low-voltage battery pack  10 . Each battery interface  130  includes a pair of rails  132 , a positive electrode input terminal  134   a , a negative electrode input terminal  134   b , a battery controller input/output terminal  136  and a latch receiving hole  138 . The battery interface  130  is substantially identical to the battery interface  60  of the above-described low-voltage electric tool  50  in terms of the respective structures. The two battery interfaces  130  are arranged side by side in the rear portion of the main body  102 , and the low-voltage battery packs  10  can be inserted in the same direction. The two low-voltage battery packs  10  attached to the two battery interfaces  130  are connected in series and supply current to the circuitry of the main body  102  at about 36 volts. 
     The main body  102  of the high-voltage electric tool  100  also includes two indicators  160  respectively positioned above the two battery interfaces  130 . Each indicator  160  comprises, e.g., one or more light-emitting diodes, or another means for visually communicating battery condition information to the tool user, such as but not limited to one or more incandescent lamps and/or a display, such as an LCD. In a preferred embodiment, one of the indicators  160  may indicate a charge state or level of charge of the low-voltage battery pack  10  attached to one battery interface  130 , and the other indicator  160  may indicate the same condition (i.e. level of charge) or another condition of the low-voltage battery pack  10  attached to the other battery interface  130 . More preferably, both indicators  160  indicate the charge state or the level of charge of the corresponding low-voltage battery pack  10 . For example, the light-emitting diode can be illuminated when the charge state drops to a level at which recharging of the battery pack  10  is necessary. It is further preferred that each indicator  160  indicates the charge state of its corresponding low-voltage battery pack  10  at least in two levels, e.g., a yellow “low-charge warning” and red “immediately stop tool use” indication. A third green “tool operation permitted” LED also may be optionally provided, so that the tool user can receive visual confirmation that the battery is in a suitable condition for use. It is also preferred that one or more indicators  160  communicate information concerning a possible battery temperature abnormality (e.g., overheating) of the corresponding low-voltage battery pack  10 , instead of or in addition to the charge state of the corresponding low-voltage battery pack  10 . 
     As shown in  FIG.  2   , the two indicators  160  are arranged side by side on a rear surface  102   a  of the high-voltage electric tool  100  and have the same indication direction (that is, the direction of illumination of the two light-emitting diodes is the same or substantially the same). Therefore, the user can see both indicators  160  simultaneously and can simultaneously recognize the respective charge states of the two low-voltage battery packs  10  in a convenient and reliable manner. Further, the indicators  160  are disposed above the corresponding battery interfaces  130 . Therefore, for example, if the high-voltage electric tool  100  abruptly stops, the user can immediately and conveniently determine which of the low-voltage battery packs  10  has experienced a problem or abnormality. In addition or in the alternative to the rear surface  102   a , the two indicators  160  could be disposed in other locations that can be simultaneously viewed by the user, such as an upper surface of the main body  102 . More particularly, it is preferred that the two indicators  160  are disposed generally in the same plane, so that the user can simultaneously see the two indicators  160  from various different directions. 
     In addition or in the alternative, one or more indicators  160  can be also provided on an outer surface of each low-voltage battery pack  10 , e.g. a surface of the battery pack  10  that faces rearward when the battery pack  10  is attached to the tool  100 . As was already explained above, it is preferred that the two battery interfaces  130  are arranged side by side and can slidably receive the low-voltage battery packs  10  in the same direction. In such an embodiment, when the two low-voltage battery packs  10  are attached to the main body  102 , the two indicators  160  will be positioned side by side in the same plane and the indication or illumination direction thereof will also be the same or substantially the same. As a result, even if the indicators  160  are disposed on the respective battery packs  10 , the user can simultaneously view the two indicators  160  from various different directions. 
     An exemplary electric circuit for the high-voltage electric tool  100 , as well as for the two low-voltage battery packs  10  serving as the power source for the tool  100 , will be explained below with reference to  FIG.  5   . Each low-voltage battery pack  10  comprises five battery cells  16  connected in series and a battery controller  18 , preferably a microprocessor. Each cell  16  is preferably a lithium-ion cell and the nominal voltage thereof is 3.6 volts. The five cells  16  connected in series are connected to the positive electrode output terminal  24   a  and negative electrode output terminal  24   b , and current can flow across the two terminals  24   a ,  24   b  at a voltage of about 18 volts. As shown in  FIG.  5   , the negative electrode output terminal  24   b  of the upper low-voltage battery pack  10  is electrically connected to the positive electrode output terminal  24   a  of the lower low-voltage battery pack  10  via the terminals  134   a  and  134   b , which are conductively connected by a wire. As a result, when the two low-voltage battery packs  10  are connected to the respective battery interfaces  130 , the battery cells  16  of the two low-voltage (18 volt) battery packs  10  are connected in series and supply current to the circuitry of the main body  102  at a voltage of about 36 volts. 
     The battery controller  18  preferably comprises an integrated circuit that includes a CPU and can execute various programs stored therein. The battery controller  18  is electrically connected to each cell  16  and can measure the voltage of each cell  16 . The battery controller  18  may be programmed to perform an algorithm, wherein the controller  18  determines the charge state or level of charge of each cell  16  based on the measured voltage of each cell  16 , compares the measured voltage to a predetermined, stored threshold value and then outputs an autostop signal (AS signal) to the autostop terminal  26  when at least one cell  16  is determined to require recharging based upon the comparison step. In this case, the autostop signal may be a signal, e.g., indicating that a high impedance has been detected. In this embodiment, and all other embodiments disclosed herein, the autostop signal may preferably be a digital logic signal that is selected from one of two different voltage levels, i.e. a “1” or “0” digital signal that has a distinctly different voltage level signal as compared to a “battery normal” signal. However, it is also contemplated that the battery controller  18  may be an analog circuit or a mixed analog/digital circuit (e.g., a state machine) and the battery controller  18  may output analog signals (e.g., signals having more than two voltage levels) as the autostop signal. Naturally, the battery controller  18  is not limited to outputting only “autostop” signals, but may also be configured or programmed to output a wide variety of signals, e.g., representing one or more conditions of the battery, such as battery temperature, battery voltage, battery impedance, etc. 
     The main body  102  is provided with a motor  176  that drives the tool (in this exemplary embodiment, a blower fan). The two low-voltage battery packs  10  are connected in series with the motor  176  via a main switch  178 . The main body  102  is provided with a speed adjusting circuit  190 , a power FET  194 , a gate-voltage-controlling transistor  192 , and a voltage division circuit  196 . The power FET  194  is connected in series with the motor  176  and can shut off the electric current flowing to the motor  176 . The speed adjusting circuit  190  performs pulse width modulation control for controlling the current flow through the power FET  194  and thus can adjust the rotational speed of the motor  176  in a manner well known in the power tool field. The gate-voltage-controlling transistor  192  is connected to the gate of the power FET  194  and, together with the voltage division circuit  196 , can control the gate voltage of the power FET  194 . 
     The main body  102  is also provided with a main controller (electronic processor)  152 , a power supply circuit  142  for the main controller  152 , a shunt resistor  150  connected in series with the motor  176 , a current detection circuit  148  that detects the electric current flowing to the motor  176  based on the voltage of the shunt resistor  150 , and an autostop signal (AS signal) input/output circuit  144  that inputs/outputs autostop signals to/from the gate-voltage-controlling transistor  192 . 
     The main controller  152  is preferably an integrated circuit including a CPU and can execute various programs stored therein. For example, the main controller  152  may be programmed to perform the following algorithm. After receiving a voltage signal outputted by a current detection circuit  148  as an input signal, the main controller  152  compares the voltage signal to a pre-set, stored threshold/permissible value and then outputs an autostop signal to the gate-voltage-controlling transistor  192  via the autostop signal input/output circuit  144  when the electric current of the motor  176  exceeds the pre-set permissible value. In this case, the gate-voltage-controlling transistor  192  decreases the voltage coupled to the gate of the power FET  194  to the ground voltage, thereby shutting off the power FET  194 . As a result, the motor  176  and the low-voltage battery pack  10  are electrically disconnected and an overload of the motor  176  and the low-voltage battery pack  10  may be prevented. A fuse  162  for preventing an excessive current from flowing between the motor  176  and the low-voltage battery pack  10  may also optionally be provided in the circuit path between the motor  176  and the low-voltage battery pack  10 . 
     The main controller  152  is electrically connected to the battery controller input/output terminal (hereinafter “autostop terminal”)  136  of the battery interface  130  and can receive a signal voltage (for example, an autostop signal) from the battery controller  18  as an input signal and can output a signal voltage (for example, a discharge protection cancellation signal) to the battery controller  18 . In this case, because two low-voltage battery packs  10  are connected in series, the reference voltages (ground voltages) of the two low-voltage battery packs  10  differ from each other. More specifically, whereas the reference voltage of the low-voltage battery pack  10  positioned at the low-voltage side (lower side in  FIG.  5   ) will be referred to as a zero volt ground, the reference voltage of the low-voltage battery pack  10  positioned at the high-voltage side (upper side in  FIG.  5   ) is 18 volts due to the series connection via terminals  24   a ,  134   a ,  134   b ,  24   b . The reference voltage of the main body  102  is equal to the reference voltage of the low-voltage battery pack  10  at the low-voltage side and is thus also zero volts. As a result, the levels of the inputted and outputted signal voltages differ significantly between the main controller  152  of the main body  102  and the battery controller  18  of the upper low-voltage battery pack  10  positioned at the high-voltage side. Consequently, the signal voltages cannot be directly inputted and outputted between the controllers  18 ,  152  unless a conversion (e.g., a step-down, step-up or other voltage level shift) of the signal voltages is first performed. 
     To overcome this problem, the high-voltage electric tool  100  of the present embodiment also includes two voltage level-shifters (e.g., DC-to-DC converters)  154   b ,  156   b  provided between the battery controller  18  of the low-voltage battery pack  10  positioned at the high-voltage side and the main controller  152  of the main body  102 . One level-shifter  154   b  is provided on a conductive path  154  that conducts a signal voltage from the main controller  152  to the battery controller  18  and raises falters), preferably proportionally raises, the level of the signal voltage outputted by the main controller  152  to an acceptable or readable level for the battery controller  18 . The other level-shifter  156   b  is provided on a conductive path  156  for conducting a signal voltage from the battery controller  18  to the main controller  152  and lowers (alters), preferably proportionally lowers, the level of the signal voltage outputted by the battery controller  18  to an acceptable or readable level for the main controller  152 . As a result, signals can be communicated (i.e. input and output) between the battery controller  18  and the main controller  152  without any problem caused by the different ranges of voltages at which the two controllers  18 ,  152  operate. 
     Further, cut-off switches  154   a ,  156   a  are also provided between each battery controller  18  and the main controller  152 . One cut-off switch  154   a  is provided on the conductive path  154  for conducting the signal voltage from the main controller  152  to the battery controller  18 , and the other cut-off switch  156   a  is provided on the conductive path  156  for conducting a signal voltage from the battery controller  18  to the main controller  152 . The cut-off switches  154   a ,  156   a  are controlled by the main controller  152 . When the main controller  152  determines that the high-voltage electric tool  100  has not been used for a predetermined time, the main controller  152  switches off the cut-off switches  154   a ,  156   a , thereby electrically disconnecting the battery controllers  18  from the main controller  152 . As a result, leakage current is prevented from flowing for too long of a time between the battery controllers  18  and the main controller  152 , thereby preventing the low-voltage battery pack  10  from being excessively discharged. The cut-off switches  154   a  and  156   b  are electrically connected between the main controller  152  and respective battery controllers  18  via the respective wires  154 ,  156 , through which a leakage current may flow. 
     It should be understood that the arrangement of the cut-off switch(es) of the present teachings is not limited to the arrangement shown in the present embodiment. For example, if there are a plurality of wires, through which a leakage current may possibly flow between the main controller  152  and one battery controller  18 , the cut-off switch(s) may be provided in one or some, but not all, of the conductive paths. In another alternative embodiment, in which a plurality of battery packs is connected to the main controller, the cut-off switch(s) may be provided between the main controller  152  and only one or some of the battery packs (e.g., only the first battery pack # 1  or the second battery pack # 2 ). 
     As described hereinabove, when the charge state of the cells  16  is detected as having decreased below a pre-determined threshold, the battery controller  18  outputs an autostop signal to the autostop terminal  26 , which is electrically connected to the autostop terminal  136 . The autostop signal outputted from the battery controller  18  is input into the main controller  152  via the conductive path  156 . The main controller  152  receives the autostop signal from the battery controller  18  and outputs an autostop signal to the gate-voltage-controlling transistor  192 . In this case, the autostop signal outputted by the main controller  152  is conducted to the gate of the gate-voltage-controlling transistor  192  via an autostop signal input/output circuit  144 . As a result, the gate-voltage-controlling transistor  192  is turned on (i.e. becomes conductive), the power FET  194  is shut off, and current supply to the motor  176  is stopped. The low-voltage battery pack  10  is thus prevented from being over or excessively discharged. 
     In addition, when the main controller  152  receives the autostop signal from the battery controller  18 , the indicator (LED of indication circuit)  160  is preferably illuminated. In this case, the main controller  152  selectively illuminates only the indicator  160  corresponding to the low-voltage battery pack  10  that has outputted the autostop signal. As a result, the user can immediately determine which low-voltage battery pack  10  requires charging. 
     As described hereinabove, the high-voltage electric tool  100  has two battery interfaces  130  configured to removably receive respective low-voltage battery packs  10  and can simultaneously use two low-voltage battery packs  10  as the power source. The two low-voltage battery packs  10  are connected in series to the motor  176  and supply a voltage of 36 volts to the motor  176 . Thus, the high-voltage electric tool  100  with a rated voltage of 36 volts is driven by two low-voltage battery packs  10 , each having a nominal voltage of 18 volts. The user can power the high-voltage electric tool  100  by using already available low-voltage battery packs  10 , without having to purchase the high-voltage battery pack  30  and a charger therefor. Each low-voltage battery pack  10  also can be used individually as a sole power source for the low-voltage electric tool  50 . Therefore, the user can effectively use the already available low-voltage battery packs  10  and the battery charger therefor. 
       FIG.  6    illustrates an example in which the electric circuit of the high-voltage electric tool  100  has been modified. In this modified example, two bypass circuits  158  are added to the circuit shown in  FIG.  5   . One bypass circuit  158  is provided for each respective low-voltage battery pack  10  connected with the main controller  152 . Each bypass circuit  158  connects the positive electrode input terminal  134   a  with the negative electrode input terminal  134   b  for one battery pack  10  via a diode  158   a . Thus, the bypass circuit  158  connects the positive electrode output terminal  24   a  with the negative electrode output terminal  24   b  of each low-voltage battery pack  10  via the diode  158   a . In this embodiment, one bypass circuit  158  is provided for each of the battery packs  10  connected with the main controller  152 . Note that the arrangement of the bypass circuit(s) of the present teachings is/are not limited to the above embodiment. For example, the bypass circuit may be provided between only some of the battery packs (e.g., only the first battery pack # 1  or the second battery pack # 2 ). 
     The anode of the diode  158   a  is connected to the negative electrode input terminal  134   b , and the cathode of the diode  158   a  is connected to the positive electrode input terminal  134   a . Therefore, electric current normally does not flow in the diode  158   a , and the positive electrode output terminal  24   a  and the negative electrode output terminal  24   b  of the low-voltage battery pack  10  are electrically disconnected. However, when the low-voltage battery pack  10  becomes over-discharged and a reverse voltage is generated across the output terminals  24   a ,  24   b  of the low-voltage battery pack  10 , electric current is caused to flow in the diode  158   a . Thus, the output terminals  24   a ,  24   b  of the battery pack  10  become electrically connected via the bypass circuit  158 . As a result, even if only one low-voltage battery pack  10  becomes over-discharged, any damage caused to that low-voltage battery pack  10  can be minimized or even prevented. A fuse  158   b  also may be optionally provided in the bypass circuit  158 . In this case, if a large current flows in the bypass circuit  158 , the bypass circuit  158  will be physically disconnected by the fuse  158   b , which has melted or otherwise broken the connection due to the excessive current. As a result, any damage caused to the low-voltage battery pack  10  can be minimized or prevented, for example, even when Zener breakdown occurs in the diode  158   a . The fuse  158   b  is preferably accessible by the user so that it can be replaced, in case it is broken. 
       FIG.  7    illustrates another modified example of the electric circuit of the high-voltage electric tool  100 . In this modified example, the attachment position of the power supply for the main controller  152  in the circuit shown in  FIG.  5    has been changed. As shown in  FIG.  7   , the main switch  178  is inserted between the low-voltage battery pack  10  and the power supply circuit  142 . Thus, when the main switch  178  is switched off, the current flow to the main controller  152  is simultaneously shut off. As a result, the main controller  152  can be prevented from unnecessarily consuming power in an inactive state of the high-voltage electric tool  100 . 
       FIG.  8    illustrates another modified example of the electric circuit of the high-voltage electric tool  100 . In this modified example, two bypass circuits  158  are added to the circuit shown in  FIG.  7   . The structure, functions, and effect of the bypass circuits  158  are same as described with reference to the embodiment shown in  FIG.  6   . 
     Two types of adapters  200 ,  300  are also disclosed in the present teachings, namely a corded adapter  200  and an integrated adapter  300 . The corded adapter  200  will be explained first with reference to  FIGS.  9 ,  10 , and  11   . The tool shown in  FIGS.  9  and  10    corresponds to the tool  70  shown in  FIGS.  19 - 22   , which was described above and is incorporated herein by reference. As shown in  FIG.  9   , the adapter  200  is configured to connect a plurality of low-voltage battery packs  10  to the high-voltage electric tool  70 . The adapter  200  is provided with a main body side unit  202  configured to be detachably attached to the main body  72  of the high-voltage electric tool  70 , a pack side unit  206  configured to removably receive or attach a plurality of low-voltage battery packs  10 , and an electric cord  204  that physically and electrically connects the main body side unit  202  to the pack side unit  206 . An attachment hook  206   a  optionally may be provided on the pack side unit  206  to enable it to be attached to the user&#39;s clothing or belt or another article supported by the user&#39;s body, so that the adapter  200  and attached battery packs  10  can be conveniently carried during operation of the tool  70 . 
     As shown in  FIG.  10   , the main body side unit  202  has an outer contour that generally conforms to the outer contour of the high-voltage battery pack  30 . A connector  220  is provided on the main body side unit  202  in the same manner as on the high-voltage battery pack  30 . The connector  220  can be slidingly inserted into the battery interface  80  provided on the main body  72  of the high-voltage electric tool  70 . The connector  220  includes a pair of rails  222 , a positive electrode output terminal  224   a , a negative electrode output terminal  224   b , and an autostop terminal  226 . When the main body side unit  202  is attached to the battery interface  80 , the positive electrode output terminal  224   a  of the main body side unit  202  is connected to the positive electrode input terminal  84   a  of the battery interface  80 , and the negative electrode output terminal  224   b  of the main body side unit  202  is connected to the negative electrode input terminal  84   b  of the battery interface  80 . Further, the autostop terminal  226  is connected to the battery controller input/output (autostop) terminal  86 . As a result, the main body side unit  202  is electrically connected to the internal circuitry of the main body  72  of the high-voltage electric tool  70 . Further, the main body side unit  202  has a latch member  212  that is engaged with the latch receiving hole  88  (see  FIG.  22   ) of the battery interface  80  and is configured to detachably affix the main body side unit  202  to the battery interface  80 . This engagement of the latch receiving hole  88  with the latch member  212  can be released by the latch release button  214 . 
     As shown in  FIG.  11   , the pack side unit  206  includes two battery interfaces (two battery pack receptacles)  230 . Each battery interface  230  can removably receive or attach one low-voltage battery pack  10 , and the low-voltage battery pack  10  can be slidably received thereby. Each battery interface  230  has a pair of rails  232 , a positive electrode input terminal  234   a , a negative electrode input terminal  234   b , a battery controller input/output (autostop) terminal  236  and a latch receiving hole  238 . With respect to the structure, each battery interface  230  is substantially identical to the battery interface  60  of the low-voltage electric tool  50  explained hereinabove with respect to  FIGS.  17  and  18    and incorporated herein by reference. The two battery interfaces  230  are arranged side by side on the lower surface of the pack side unit  206  and the low-voltage battery packs  10  are respectively inserted therein in the same direction. The two low-voltage battery packs  10  attached to the pack side unit  206  are connected in series to the positive electrode output terminal  224   a  and the negative electrode output terminal  224   b  of the connector  220 . As a result, the two low-voltage battery packs  10  supply current to the internal circuitry of the main body  72  of the high-voltage electric tool  70  at a voltage of about 36 volts. The adapter  200  enables the power tool  70  having the battery interface  80  dedicated for the high-voltage battery pack  30  to be connected to the low-voltage battery packs  10  and to be driven thereby. In addition, the autostop terminal  26  of the battery pack  10  is connected to the autostop terminal  236  of the pack side unit  206 . 
     As shown in  FIG.  11   , the pack side unit  206  also includes two indicators  260 . The two indicators  260  are respectively positioned above the two battery interfaces  230 . Each indicator  260  is for example a light-emitting diode, but may be any other device that is capable of visually communicating information about the status of the attached battery pack  10 , such as one or more incandescent lamps or one or more LCDs. The teachings concerning the indicator  160  discussed above with respect to the embodiment of  FIGS.  2 - 4    are equally applicable to the present embodiment and thus the above-teachings concerning the indicator  160  are incorporated herein. Thus, for example, one indicator  260  may indicate a charge state or level of charge of the low-voltage battery pack  10  attached to one battery interface  230 , and the other indicator  260  may indicate the same condition (level of charge) or another condition of the low-voltage battery pack  10  attached to the other battery interface  230 . Each indicator  260  preferably indicates at least the charge state of its corresponding low-voltage battery pack  10 . For example, the light-emitting diode can be illuminated when the charge state drops below a level at which recharging becomes necessary. Like the indicator  160 , it is again preferred that the indicator  260  indicates the charge state of its corresponding low-voltage battery pack  10  at least in two levels. Also similar to the indicator  160 , it is again preferred that the indicator  260  indicates a temperature abnormality of its corresponding low-voltage battery pack  10 , instead of or in addition to the charge state thereof. 
     The two indicators  260  are preferably arranged side by side on one surface of the pack side unit  206  and have the same or substantially the same indication direction (that is, the same or substantially the same illumination direction of light-emitting diodes). Therefore, the user can see the two indicators  260  simultaneously and can simultaneously recognize the charge states of the two low-voltage battery packs  10 . Further, the indicators  260  are preferably disposed above the corresponding battery interfaces  230 . Therefore, for example, if the high-voltage electric tool  70  abruptly stops, the user can immediately determine which low-voltage battery pack  10  has experienced a problem or abnormality. The two indicators  260  can be also disposed, for example, on the main body side unit  202 , rather than on the pack side unit  206 . The two indicators  260  can be also arranged in other locations that can be simultaneously viewed by the user. It is preferred that the two indicators  260  are disposed in the same plane, so that the user can simultaneously see the two indicators  260  from various directions. 
     Similar to the indicator  160 , the indicator  260  can be also provided in each low-voltage battery pack  10 . As has already been explained above, the two battery interfaces  230  are arranged side by side and can receive the low-voltage battery packs  10  in the same direction. Therefore, when the two low-voltage battery packs  10  are attached to the pack side unit  206 , the two indicators  260  are positioned side by side in the same plane and the direction of illumination is also the same. The user can thus simultaneously view the two indicators  260  from various directions. 
     An exemplary electric circuit of the adapter  200  will be explained below with reference to  FIG.  12   . As will be readily understood from a comparison of  FIG.  12    with  FIG.  5   , the circuit of the adapter  200  is substantially identical to a part of the circuit disposed in the main body  102  of the above-described high-voltage electric tool  100 . More specifically, a combination of the circuit of the main body  72  of the high-voltage electric tool  70  and the circuit of the adapter  200  shown in  FIG.  12    is substantially identical to the circuit of the main body  102  of the high-voltage electric tool  100  shown in  FIG.  5    (however, the power FET  246  is absent in  FIG.  5   ). 
     First, the circuit of the main body  72  of the high-voltage electric tool  70  shown in FIG.  12  will be explained. The main body  72  of the high-voltage electric tool  70  is provided with a motor  76 , a main switch  78 , a speed adjusting circuit  90 , a power FET  94 , a gate-voltage-controlling transistor  92 , and a voltage division circuit  96 . The configurations of these components may be identical to those of the motor  176 , main switch  178 , speed adjusting circuit  190 , power FET  194 , gate-voltage-controlling transistor  192 , and voltage division circuit  196  of the main body  102  of the high-voltage electric tool  100  described above with reference to  FIGS.  5 - 8    and therefore an explanation thereof is not necessary here. Two low-voltage battery packs  10  are thus connected in series to the motor  76  via the adapter  200 . 
     The adapter  200  is provided with a main controller  252 , a power source circuit  242 , a shunt resistor  250 , a current detection circuit  248 , an autostop signal input/output circuit  244 , and a fuse  262 . The main controller  252  is electrically connected to two indicators  260 . The configurations of these components may be identical to those of the main controller  152 , power source circuit  142 , shunt resistor  150 , current detection circuit  148 , autostop signal input/output circuit  144 , indicator  160 , and fuse  162  in the main body  102  of the high-voltage electric tool  100  and therefore an explanation thereof also is not necessary here. 
     The adapter  200  is further provided with a power FET  246  between a negative electrode input terminal  234   b  connected to the low-voltage battery pack  10  and a negative electrode output terminal  224   b  connected to the high-voltage electric tool  70 . Thus, two low-voltage battery packs  10  are electrically connected to the motor  76 , and a discharge current produced by the two series-connected low-voltage battery packs  10  flows through this circuit. The main controller  252  is connected to the gate of the power FET  246  and can control the power FET  246 . For example, the main controller  252  may shut off the power FET  246  when the output voltage of the current detection circuit  248  exceeds a predetermined value. 
     The functions of the power FET  246  will be explained below. When the adapter  200  is detached from the high-voltage electric tool  70 , the connector  220  of the adapter  200  is exposed. When the two low-voltage battery packs  10  are attached to the adapter  200  in this state, a voltage of about 36 volts is generated across the positive electrode output terminal  224   a  and the negative electrode output terminal  224   b  in the connector  220 . The positive electrode output terminal  224   a  and the negative electrode output terminal  224   b  are disposed in a slot of the adapter  200  as shown in  FIG.  10   . Therefore, foreign matter is generally prevented from coming into contact with the two output terminals  224   a ,  224   b . However, the possibility of the foreign matter coming into contact with the two output terminals  224   a ,  224   b  cannot be completely excluded. For example, if the two output terminals  224   a ,  224   b  were to be short-circuited by foreign matter, a very large current flow could be generated inside the low-voltage battery pack(s)  10  or adapter  200 . In the circuit according to the present embodiment, the power FET  246  is provided inside the adapter  200  so that, after the adapter  200  has been removed from the high-voltage electric tool  70 , if very large current is detected, the circuit and thus the current flow can be cut off by the power FET  246 . 
     The main controller (electronic processor)  252  is electrically connected to an autostop terminal  236  of each battery interface  230  and can receive an input signal voltage (for example, an autostop signal) from the battery controller  18  and can output a signal voltage (for example, a discharge protection cancellation signal) to the battery controller  18 . Cut-off switches  254   a ,  256   a  are provided, respectively, in a conductive path  254  that conducts the signal voltage from the main controller  252  to the battery controller  18  and in a conductive path  256  that conducts a signal voltage from the battery controller  18  to the main controller  252 . Further, level-shifters  254   b ,  256   b  are also provided in the conductive paths  254 ,  256 , respectively, in order to adjust (alter) the voltage of signals output from the battery controller  18  of the low-voltage battery pack  10  that is positioned on the high-voltage side, as was discussed above with respect to the exemplary level shifters  154   b ,  156   b  of  FIGS.  5 - 8   . Thus, the cutoff switches  154   a ,  156   a  and level shifters  154   b ,  156   b  described above with respect to the high-voltage electric tool  100  may be used without modification in the present embodiment and therefore an explanation thereof is not necessary here. 
     As described hereinabove, by using the adapter  200 , the high-voltage electric tool  70  (which is designed to normally attach only one battery pack at the battery interface  80 ) can be operated with two low-voltage battery packs  10 . By connecting the two low-voltage battery packs  10  in series to the motor  76 , it is possible to supply a voltage of about 36 volts to the motor  76 . As a result, the high-voltage electric tool  70  with a rated voltage of 36 volts can be driven by two low-voltage battery packs  10 , each having a nominal voltage of 18 volts. Thus, the high-voltage electric tool  70  can be operated using already available low-voltage battery packs  10 , without the need to purchase a high-voltage battery pack  30  that supplies a nominal voltage of 36 volts or the charger therefor. Each low-voltage battery pack  10  can also be individually used as the sole power source for the low-voltage electric tool  50 , which operates with an 18 volt battery pack. 
       FIG.  13    illustrates a modified example of the electric circuit of the adapter  200 . In this modified example, two bypass circuits  258  are added to the circuit shown in  FIG.  12   . One bypass circuit  258  is provided for each respective low-voltage battery pack  10 . The bypass circuit  258  includes a diode  258   a  and a fuse  258   b . These bypass circuits  258  may be identical to the bypass circuits  158  of the high-voltage electric tool  100  described above with respect to  FIGS.  6  and  8    and therefore an explanation thereof is not necessary here. 
     Another (integrated) adapter  300  will be explained below with reference to  FIGS.  14 ,  15   , and  16 . The tool shown in  FIGS.  14 - 16    corresponds to the tool  70  shown in  FIGS.  19 - 22   , which was described above and is incorporated herein by reference. As shown in  FIG.  14   , the adapter  300  also serves to connect a plurality of low-voltage battery packs  10  to the high-voltage electric tool  70 . Similar to the adapter  200 , the adapter  300  also enables the power tool  70  having the battery interface  80  designed to receive the high-voltage battery pack  30  to be connected to the low-voltage battery packs  10  and to be driven thereby. In contrast with the above-described adapter  200 , the entire circuitry for this adapter  300  is contained within one housing. That is, the portions, which correspond to the main body side unit  202  and pack side unit  206  of the above-described adapter  200 , are integrated into a single housing. The electric circuitry of the adapter  300  may be functionally identical to the circuitry of the above-described adapter  200  shown in  FIG.  12    or  FIG.  13   . 
     As shown in  FIG.  15   , the connector  220  may be provided at or on the upper surface of the adapter  300  in the same manner as the connector  220  of the corded adapter  200  shown in  FIG.  10   . Thus, the connector  220  can be slidingly inserted into the battery interface  80  provided on the main body  72  of the high-voltage electric tool  70 . The connector  220  includes a pair of rails  222 , a positive electrode output terminal  224   a , a negative electrode output terminal  224   b , and an autostop terminal  226 . The structures of connectors  220  in the two types of adapters  200 ,  300  may be substantially identical. Thus, when the connector  220  of the adapter  300  is attached to the battery interface  80 , the positive electrode output terminal  224   a  of the adapter  300  is electrically connected to the positive electrode input terminal  84   a  of the battery interface  80 , and the negative electrode output terminal  224   b  of the adapter  300  is electrically connected to the negative electrode input terminal  84   b  of the battery interface  80 . As a result, the adapter  300  is electrically connected to the circuitry contained in the main body  72  of the high-voltage electric tool  70 . In addition, the autostop terminal  86  is connected to the autostop terminal  226 . 
     As shown in  FIG.  16   , two battery interfaces (two battery pack receptacles)  230  are provided on the lower surface of the adapter  300  in the same manner as the battery interfaces  230  of the corded adapter  200  shown in  FIG.  11   . Each battery interface  230  can removably receive or attach one low-voltage battery pack  10 , and the low-voltage battery pack  10  can be slidably received thereby. Each battery interface  230  has a pair of rails  232 , a positive electrode input terminal  234   a , a negative electrode input terminal  234   b , and a latch receiving hole  238 . The structures of the battery interfaces  230  of the two types of adapters  200 ,  300  may be substantially identical. The two battery interfaces  230  are arranged side by side on the lower surface of the pack side unit  206  and the low-voltage battery packs  10  are respectively inserted therein in the same direction. The two low-voltage battery packs  10  attached to the adapter  300  are connected in series to the positive electrode output terminal  224   a  and the negative electrode output terminal  224   b  of the connector  220 . As a result, the two low-voltage battery packs  10  supply current to the circuitry contained in the main body  72  of the high-voltage electric tool  70  at a voltage of about 36 volts. In addition, the autostop terminals  26  of the battery pack  10  are respectively connected to the autostop terminals  236  of the adapter  300 . 
     As shown in  FIG.  15   , the adapter  300  is also provided with two indicators  260 . The two indicators  260  are disposed on the rear surface  300   a  of the adapter  300 . The two indicators  260  are respectively positioned above the two battery interfaces  230 . Each indicator  260  comprises, e.g., a light-emitting diode or another light source, such as an incandescent light, or a display device such as an LCD, as was described above with reference to the indicator  260  of the corded adapter  200  and the indicator  160  of the embodiment of  FIGS.  2 - 4   , which description is again incorporated herein by reference. Thus, similar to the above embodiments, the indicator  260  may indicate a charge state of the low-voltage battery pack  10  attached to one battery interface  230 , and the other indicator  260  may indicate the same or a different condition of the low-voltage battery pack  10  attached to the other battery interface  230 . The two indicators  260  are preferably arranged side by side on the rear surface  300   a  of the adapter  300 . Therefore, the user can see the two indicators  260  simultaneously and can simultaneously recognize the respective charge states or other indicated condition(s) of the two low-voltage battery packs  10 . Further, the indicators  260  are preferably disposed above the corresponding battery interfaces  230 . Therefore, for example, if the high-voltage electric tool  70  abruptly stops, the user can immediately determine which low-voltage battery pack  10  is experiencing a problem or abnormality. 
     As described hereinabove, by using the adapter  300 , the high-voltage electric tool  70  can be operated using two low-voltage battery packs  10 . By connecting the two low-voltage battery packs  10  in series to the motor  76 , it is possible to supply a voltage of about 36 volts to the motor  76 . As a result, the high-voltage electric tool  70  with a rated voltage of 36 volts can be driven by two low-voltage battery packs  10 , each having a nominal voltage of 18 volts. Thus, the high-voltage electric tool  70  can be powered using already available low-voltage battery packs  10 , without the need to purchase a high-voltage battery pack  30  having a nominal voltage of 36 volts or a charger therefor. Each low-voltage battery pack  10  can be also individually used as the sole power source for the low-voltage electric tool  50 . 
     In the present description, the representative example of the low-voltage electric tool  50  is an electric drill, and the representative example of the high-voltage electric tools  70 ,  100  is an electric blower (leaf blower). However, the present teachings are not particularly limited to these types of electric tools and can be widely applied to a variety of types of electric tools, as was described above in the Summary section. 
     Specific embodiments of the present teachings are described above, but these embodiments merely illustrate some representative possibilities for utilizing the present teachings and do not restrict the claims thereof. The subject matter set forth in the claims includes variations and modifications of the specific examples set forth above. 
     The technical elements disclosed in the specification or the drawings may be utilized separately or in other combinations that are not expressly disclosed herein, but will be readily apparent to a person of ordinary skill in the art. Furthermore, the subject matter disclosed herein may be utilized to simultaneously achieve a plurality of objects or to only achieve one object, which object(s) may not be explicitly recited in the present disclosure. 
     Although the present teachings have been described with respect to a preferred usage of lithium-ion cells, the present teachings are, of course, applicable to any type of battery chemistry or technology, including but not limited to nickel-cadmium, nickel-metal-hydride, nickel-zinc, lithium iron phosphate, etc. 
     Further, although the representative electric power tool  100  and the adapters  200 ,  300  were illustrated as providing a serial connection of two battery packs  10 , the battery interface  80  of the tool  100  or the adapters  200 ,  300  may, of course, be modified to connect three or more battery packs  10  in series and/or in parallel. Moreover, the first battery packs  10  are not all required to have the same nominal voltage and in certain applications of the present teachings, one first battery pack  10  could have a first nominal voltage, e.g., of 12 volts, and one first battery pack  10  could have a second nominal voltage, e.g., of 18 volts, i.e. the first and second nominal voltages of the two battery packs  10  are different. In this case, it is preferable that the first battery interfaces  130 ,  230  are configured differently, so as to be able to ensure that only the appropriate battery pack is attachable thereto. In addition or in the alternative, the main controller  152  of the tool  70 ,  100  or the main controller  252  of the adapter  200 ,  300 , and its supporting circuitry, may be configured to recognize battery packs having different nominal voltages and process signals outputted from the respective CPUs of the battery packs appropriately. 
     The adapters  200 ,  300  may be modified to only provide a voltage level-shifting function and the tool motor controlling function may be performed by an integrated circuit, e.g., a microprocessor, located in the main body  72 ,  100  of the tool  70 ,  100 . For example, the adapters  200 ,  300  are not required to include the main controller  252  and instead may include, e.g., only the level-shifters  254   b ,  256   b  and/or the cut-off switches  254   a ,  256   a . Naturally, the adapters  200 ,  300  may also include the diode(s)  258   a , the fuse(s)  258   b  and the indicators  260 . In such embodiments, the functions of the main controller  252  are performed by circuitry located in the main body  72 ,  100  of the tool  70 ,  100 . In this case, the level-shifters  254   b ,  256   b  preferably supply appropriate voltage-adjusted signals from the battery pack controllers  18  to the processor located in the main body  72 ,  102 .