Patent Publication Number: US-2022231387-A1

Title: Terminal configuration for a battery pack

Description:
RELATED APPLICATION 
     This application is a division of U.S. patent application Ser. No. 15/934,798, filed Mar. 23, 2018, which claims the benefit of U.S. Provisional Patent Application No. 62/475,951, filed Mar. 24, 2017, the entire content of each of which is hereby incorporated by reference. 
    
    
     FIELD 
     The present invention relates to battery packs and electrical devices connectable to battery packs and, more particularly, to a terminal configuration for a battery pack and/or an electrical device. 
     SUMMARY 
     Tools, such as power tools (e.g., drills, drivers, saws, etc.), outdoor tools (e.g., blowers, trimmers, etc.), etc., and other electrical devices (e.g., motorized devices, non-motorized devices, chargers, etc.) (generally referred to herein as “devices” or a “device”) may transfer power (e.g., be powered by, supply power to) with rechargeable battery packs. The battery pack may be detached from a device for charging or for use with other devices. In many cases, battery packs are designed such that the same battery pack may be used with many kinds of devices. 
     Battery packs include a number of battery cells (for example, Li-ion, NiCd, NiMH, etc.) connected in a series configuration, a parallel configuration, or a combination thereof. Power terminals are connected to the battery cells. When a battery pack is connected to a device, the power terminals of the battery pack are connected to corresponding power terminals of the device, and the battery pack provides operating power to the device through the power terminals. 
     Many electrical devices include a controller to monitor and control operation (e.g., motor speed, torque output, etc.) of the device. Similarly, many battery packs include a controller to monitor and control operation (e.g., charging and discharging operations, display state-of-charge, etc.). 
     While the device controller and the battery pack controller generally operate independently of each other, communication between the controllers may be advantageous. For example, the controllers may communicate to adjust operation based on a characteristic of the device and/or of the battery pack. As another example, the device controller may communicate with the battery pack controller to authenticate the battery pack, thereby improving the operation and security of the devices. 
     In some embodiments, the power terminals may be used to provide communication between the device controller and the battery pack controller. However, this may result in noise being generated on the communication line between the controllers. In addition, the amount of information that may be exchanged may be limited by the number of terminals. Accordingly, separate communication terminals that are isolated from the power terminals may be needed to provide a low-noise communication line with sufficient information capacity between the device controller and the battery pack controller. 
     In addition, the power received from the battery pack is used to power both the load (e.g., the motor) and the device controller. While controllers used in electrical devices generally have low power requirements, they do consume power. As such, the device controller may be put into a sleep mode to avoid unnecessarily draining the battery pack to constantly power the device controller. 
     Electrical device controllers also generally have low power capacity. For example, a device load (e.g., a motor) may operate in a range of 25-35 Amps (A) or more. In contrast, a device controller may operate at well under 1 A. When initiating operation of an electrical device, it may be desirable to provide low power to “wake-up” the device controller before the full voltage of the battery pack is provided to power the electrical device. 
     In some embodiments, a separate dedicated battery (e.g., a coin cell) may be used to power low power functions of the electrical device or the battery pack. The dedicated battery may be used separately from the battery pack to power the device controller. However, such a dedicated battery adds a separate non-chargeable or non-replaceable component to the electrical device. 
     In other embodiments, low power may be provided to the electrical device through a low-power circuit connected across a single battery of the battery pack. However, this may result in cell balancing issues, as one battery cell (the “low-power cell”) is drained more often than the other battery cells in the battery pack, reducing the service life of the battery pack. In order to avoid these issues, the single cell low power application may be limited to very low power and infrequent operations. 
     Accordingly, a relatively low-power power source may be needed to power recurring low power functions of the electrical device without incurring performance or service life issues (e.g., due to cell imbalances) or adding additional non-chargeable, non-replaceable components to the battery pack or electrical device. A low-power power supply may be advantageous in powering other low-power components of an electrical device, such as an indicator/LED, a communication module, etc. 
     In one independent aspect, a battery pack may generally include a housing; a plurality of battery cells supported by the housing; a plurality of terminals including a positive power terminal, a negative power terminal, and a low power terminal; a low power circuit connecting the plurality of battery cells to the low power terminal and the negative terminal to output a first voltage; and a power circuit connecting the plurality of battery cells to the positive power terminal and the negative terminal to output a second voltage, the second voltage being greater than the first voltage (e.g., 80 V compared to 5 V). 
     In some embodiments, the low power circuit may include a transformer (e.g., a step down transformer or a low dropout regulator (LDO)). In some embodiments, the battery pack may include a controller operable to control the battery pack to selectively output the first voltage and the second voltage. 
     In another independent aspect, a method of operating a battery-powered device with a battery pack may be provided. The device may include a device housing, a load supported by the device housing, and a device controller supported by the device housing. The battery pack may include a pack housing, and a plurality of battery cells supported by the housing. The method may generally include supplying a first voltage from the plurality of battery cells to the device to power the device controller; and supplying a second voltage from the plurality of battery cells to the device to power the device. Supplying a first voltage may include, with a transformer (e.g., a step down transformer or a low dropout regulator (LDO)), reducing a voltage of the plurality of battery cells to the first voltage. 
     In yet another independent aspect, a battery pack may generally include a housing; a plurality of battery cells supported by the housing; a controller; and a plurality of terminals including a positive power terminal, a negative power terminal and a communication terminal, the communication terminal being electrically connected to the controller and operable to communicate between the controller and an external device, the communication terminal being isolated from the positive power terminal and the negative power terminal. 
     In some embodiments, the housing may include a terminal block supporting the plurality of terminals, the positive power terminal and the negative terminal being arranged in a first row, the communication terminal being arranged in a second row spaced from the first row. 
     In a further independent aspect, an electrical combination may generally include an electrical device including a device housing, a load supported by the device housing, a device controller supported by the device housing, and a plurality of device terminals including a device positive power terminal, a device negative terminal, and a device low power terminal; and a battery pack including a pack housing; a plurality of battery cells supported by the pack housing, a plurality of pack terminals including a pack positive power terminal electrically connectable to the device positive power terminal, a pack negative power terminal electrically connectable to the device negative terminal, and a pack low power terminal electrically connectable to the device low power terminal, a low power circuit connecting the plurality of battery cells to the low power terminal and the pack negative terminal to output a first voltage to power the device controller, and a power circuit connecting the plurality of battery cells to the pack positive power terminal and the pack negative terminal to output a second voltage to power the load, the second voltage being greater than the first voltage. 
     In another independent aspect, a terminal for one of a battery pack and an electrical device electrically connectable to the battery pack along an axis may be provided. The terminal may generally include a terminal blade extending along the axis and having opposite axially-extending faces connected by opposite axially-extending edges; and a terminal support portion extending transverse to the axis and beyond an associated face. 
     In some embodiments, the terminal support portion may include a transverse wing connected to one edge. In some embodiments, the support portion includes at least one rib on the associated face. 
     In yet another independent aspect, a terminal block for one of a battery pack and an electrical device electrically connectable to the battery pack along an axis may be provided. The terminal block may generally include a housing; and a plurality of terminals including a positive power terminal and a ground terminal, at least one terminal including a terminal blade extending along the axis and having opposite axially-extending faces connected by opposite axially-extending edges, and a terminal support portion extending transverse to the axis and beyond an associated face. 
     In a further independent aspect, an electrical combination may generally include a battery pack including a pack housing, a plurality of battery cells supported by the pack housing, and a pack terminal electrically connected to the battery cells; and an electrical device including a device housing, a circuit supported by the device housing, and a device terminal electrically connected to the circuit and electrically connectable to the pack terminal to electrically connect the circuit to one or more battery cells; one of the pack terminal and the device terminal including a terminal blade extending along the axis and having opposite axially-extending faces connected by opposite axially-extending edges, and a terminal support portion extending transverse to the axis and beyond an associated face. 
     Other independent aspects of the invention may become apparent by consideration of the detailed description, claims and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a battery pack. 
         FIG. 2  is a plan view of a terminal block of the battery pack of  FIG. 1 . 
         FIG. 3  is a block diagram of the battery pack of  FIG. 1 . 
         FIG. 4  is a circuit diagram of a low-current supply circuit of a low-power circuit of the battery pack of  FIG. 1 . 
         FIG. 5  is a block diagram of a voltage regulator of the low-current supply circuit of  FIG. 4 . 
         FIG. 6  is a circuit diagram of a low-current supply circuit of a low-power circuit of the battery pack of  FIG. 1 . 
         FIG. 7  is a block diagram of a high-current supply circuit of a low-power circuit of the battery pack of  FIG. 1 . 
         FIG. 8  is a circuit diagram of a startup circuit of the high-current supply circuit of  FIG. 7 . 
         FIG. 9  is a plan view of a terminal block of an electrical device. 
         FIG. 10  is a block diagram of the electrical device. 
         FIG. 11  is a plan view of a terminal block of a charger. 
         FIG. 12  is a block diagram of the charger. 
         FIG. 13  is a flowchart illustrating a quick re-authentication process between a battery pack and an electrical device. 
         FIG. 14  is a flowchart illustrating a transmitter function of a battery transceiver of the battery pack of  FIG. 1 . 
         FIG. 15  is a flowchart illustrating a receiver function of a battery transceiver of the battery pack of  FIG. 1 . 
         FIG. 16  is an isometric view of a terminal block of an electrical device. 
         FIG. 17  is an isometric view of a terminal block of the battery pack of  FIG. 1 . 
         FIG. 18  is an isometric view of a terminal block of an electrical device. 
         FIG. 19  is a perspective view of a connection between the terminal block of the power of  FIG. 18  with a terminal block of the battery pack of  FIG. 1 . 
         FIG. 20  is a perspective view of a connection between the terminal block of the power of  FIG. 18  with a terminal block of the battery pack of  FIG. 1 . 
         FIG. 21  is a perspective view of a terminal block portion of an electrical device. 
         FIG. 22  is another perspective view of the terminal block portion of  FIG. 21 . 
         FIG. 23  is an isometric view of a terminal block of an electrical device. 
         FIG. 24  is a perspective view of a portion of an electrical device. 
         FIG. 25  is a side view of the portion of the electrical device as shown in  FIG. 24 . 
         FIG. 26  is a perspective view of power terminals shown in  FIG. 24 . 
     
    
    
     DETAILED DESCRIPTION 
     Before any independent embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other independent embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. 
     The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
     Also, the functionality described herein as being performed by one component may be performed by multiple components in a distributed manner. Likewise, functionality performed by multiple components may be consolidated and performed by a single component. Similarly, a component described as performing particular functionality may also perform additional functionality not described herein. For example, a device or structure that is “configured” in a certain way is configured in at least that way but may also be configured in ways that are not listed. 
     Furthermore, some embodiments described herein may include one or more electronic processors configured to perform the described functionality by executing instructions stored in non-transitory, computer-readable medium. Similarly, embodiments described herein may be implemented as non-transitory, computer-readable medium storing instructions executable by one or more electronic processors to perform the described functionality. As used in the present application, “non-transitory computer-readable medium” comprises all computer-readable media but does not consist of a transitory, propagating signal. Accordingly, non-transitory computer-readable medium may include, for example, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a RAM (Random Access Memory), register memory, a processor cache, or any combination thereof. 
     Many of the modules and logical structures described are capable of being implemented in software executed by a microprocessor or a similar device or of being implemented in hardware using a variety of components including, for example, application specific integrated circuits (“ASICs”). Terms like “controller” and “module” may include or refer to both hardware and/or software. Capitalized terms conform to common practices and help correlate the description with the coding examples, equations, and/or drawings. However, no specific meaning is implied or should be inferred simply due to the use of capitalization. Thus, the claims should not be limited to the specific examples or terminology or to any specific hardware or software implementation or combination of software or hardware. 
     As shown in  FIG. 1 , a battery pack  100  includes a housing  105  with a support portion  110  and a terminal block  115 . The housing  105  encloses components of the battery pack  100  including battery cells, a battery controller, etc. The support portion  110  provides a slide-on arrangement with a projection/recess  120  cooperating with a complementary recess/projection (not shown) of an electrical device (e.g., a power tool, an outdoor tool, etc.) or other electrical device (again, generally referred to herein as “devices” or a “device”) to mechanically connect the battery pack  100  and the device. 
     With reference to  FIG. 2 , the terminal block  115  is operable to electrically connect the battery pack  100  and the electrical device and, as illustrated, includes a positive battery terminal  205 , a ground terminal  210 , a charger terminal  215 , a low-power terminal  220 , a positive transmission terminal  225 , a negative transmission terminal  230 , a positive receiver terminal  235 , and a negative receiver terminal  240 . The positive battery terminal  205  and the ground terminal  210  are connectable to power terminals of an electrical device, and provide a main discharging current for the operation of the electrical device. The charger terminal  215  and the ground terminal  210  are connected to charging terminals of a charger and receive charging current to charge the battery cells of the battery pack  100 . 
     The ground terminal  210  may form a common reference between the battery pack  100  and the connected electrical device. The low-power terminal  220  provides a low-power voltage supply to the electrical device to power certain functions of the electrical device. For example, the low-power voltage supply may be used to power a device controller, indicators (e.g., LEDs), a communication module, etc. of the electrical device. 
     The positive transmission terminal  225 , the negative transmission terminal  230 , the positive receiver terminal  235 , and the negative receiver terminal  240  may together be referred to as “communication terminals” of the battery pack  100 . The communication terminals allow for differential communication between the battery pack  100  and a connected electrical device or charger. The illustrated communication terminals are only used to either receive or transmit data but not both. In other embodiments, the communication terminals follow a full-duplex standard (for example, RS485 standard). 
     In the illustrated construction, the communication terminals  225 ,  230 ,  235 ,  240  are isolated from the power terminals  205 ,  210 ,  215 ,  220  to provide a low-noise communication line. The communication terminals  225 ,  230 ,  235 ,  240  provide sufficient information capacity between the device controller and the battery pack controller. 
       FIG. 3  is a simplified block diagram of the battery pack  100 . The battery pack  100  includes battery cells  305 , a battery controller  310 , a battery memory  315 , a low-power circuit  320 , other components  325 , and a battery transceiver  330 . The battery cells  305  may be any rechargeable battery cell chemistry type, such as, for example, nickel-cadmium (NiCd), nickel-metal hydride (NiMH), Lithium (Li), Lithium-ion (Li-ion), other lithium-based chemistry, etc. In some embodiments, the battery pack  100  may include two or more battery cell strings connected in parallel, each having a number (e.g., five or more) of battery cells connected in series to provide a desired discharge output (e.g., nominal voltage (e.g., 20 V, 40 V, 60 V, 80 V, 120 V) and current capacity). In other embodiments, other configurations of battery cells  305  are also possible. 
     In some embodiments, the battery controller  310  may be implemented as a microprocessor with a separate memory, such as the battery memory  315 . In other embodiments, the battery controller  310  may be implemented as a microcontroller (with battery memory  315  on the same chip). In other embodiments, the battery controller  310  may be implemented using multiple processors. In addition, the battery controller  310  may be implemented partially or entirely as, for example, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), etc., and the battery memory  315  may not be needed or be modified accordingly. 
     In the example illustrated, the battery memory  315  includes non-transitory, computer-readable memory that stores instructions received and executed by the battery controller  310  to carry out functionality of the battery pack  100 . The battery memory  315  may include, for example, a program storage area and a data storage area. The program storage area and the data storage area may include combinations of different types of memory, such as read-only memory and random-access memory. 
     In some embodiments, a discharging switch  335  is connected between the battery cells  305  and the positive battery terminal  205 . The battery controller  310  is operable to control (e.g., open and close) the discharging switch  335  to control discharge of the battery cells  305 . In some embodiments, a charging switch  340  may also be connected between the battery cells  305  and the charger terminal  215 . The battery controller  310  is operable to control (e.g., open and close) the charging switch  340  to control charging of the battery cells  305 . 
     The discharging switch  335  and the charging switch  340  may be implemented using bi-polar unction transistors, field-effect-transistors (FETs), etc. In some embodiments, the discharging switch  335  and the charging switch  340  may be connected on the ground-side of the battery cells  305  between the battery cells  305  and the ground terminal  210 . In some embodiments (not shown), the ground terminal  210  may be split into a charging path ground terminal and a discharging path ground terminal. 
     The low-power circuit  320  is connected between the battery cells  305  and the low-power terminal  220 . The low-power circuit  320  provides a low-power voltage supply at the low-power terminal  220  to a connected electrical device. In some embodiments, the battery controller  310  may provide control signals to the low-power circuit  320  to control the operation of the low-power circuit  320 . The low-power circuit  320  will be described in more detail below with reference to  FIGS. 4-5 . 
     Other components  325  of the battery pack  100  may include, for example, voltage monitoring circuits to monitor the discharge voltage, current monitoring circuits to monitor discharge current, temperature sensors, pressure sensors, analog front-ends for cell balancing, etc. The battery controller  310  communicates with the other components  325  to monitor (e.g., receive sensor data) or to control the operation of the other components  325 . 
     In the illustrated example, the battery transceiver  330  is implemented as a differential communication transceiver (e.g., Texas Instruments SN65HVD7 Full Duplex RS-485 Transceiver). The battery transceiver  330  receives a transmission signal  345  from the battery controller  310  and sends a receiver signal  350  to the battery controller  310 . 
     The battery transceiver  330  is also connected to the communication terminals ( 225 ,  230 ,  235 , and  240 ). When the battery pack  100  transmits a communication signal to a connected electrical device or charger, the battery controller  310  sends the transmission signal  345  in addition to a transmission enable signal  355  to the battery transceiver  330 . When the battery transceiver  330  receives the transmission enable signal  355 , the battery transceiver  330  converts the transmission signal  345  to complementary transmission signals at the positive transmission terminal  225  and the negative transmission terminal  230 . When the battery transceiver  330  receives a receiver enable signal  360  from the battery controller  310 , the battery transceiver  330  receives complementary signals from the positive receiver terminal  235  and the negative receiver terminal  240 , converts the complementary signals to a single receiver signal  350 , and sends the receiver signal  350  to the battery controller  310 . 
     In other embodiments, rather than the battery transceiver  330 , the battery pack  100  may include separate transmitting and receiving components, for example, a transmitter and a receiver. 
     A purpose of the low-power terminal  220  is to provide an independent, current limited, low-power path from which the device electronics may power up. Accordingly, the device electronics may power up in a controlled fashion. In addition, the illustrated low-power circuit  320  consists of a low-power mode and a high-power mode. The low-power mode provides a minimum amount of quiescent current when both the electrical device and the battery pack  100  are in a sleep state. During normal discharge operations, the high power mode is enabled such that all device electronics may be operational. 
       FIG. 4  is a simplified circuit diagram of one embodiment of a low-current supply circuit  400  of the low-power circuit  320 . In some embodiments, the low-current supply circuit  400  may be implemented using a shunt regulator architecture. The low-current supply circuit  400  includes a voltage loop  404  and a current loop  408  within the voltage loop  404 . The low-current supply circuit  400  receives input power from the battery cells  305  over a positive terminal  412  and a negative terminal  416 . The nominal voltage range of the input power received over the terminals  412  and  416  may be between, for example, 40 Volts (V) to 80 V. 
     A fuse  420  is connected to the positive terminal  412  to act as a circuit breaker when an excess current flows through the low-current supply circuit  400 . The fuse  420  may be rated for a current higher than a current output of the low-current supply circuit  400  to allow the low-current supply circuit  400  to momentarily allow higher current without nuisance tripping. In one example, the fuse  420  may be rated for 200 mA at 125 V to allow an output current of 100 mA without nuisance tripping of the fuse  420 . 
     The voltage loop  404  includes a field-effect-transistor (FET)  424 , a voltage divider circuit  428 , and a voltage regulator  432 . The FET  424  is connected between the battery cells  305  and the low-power terminal  220 . In the illustrated embodiment, a drain of the FET  424  is connected to the output of the fuse  420 , and the source of the FET  424  is connected to the low-power terminal  220 . Pull up resistors  436  and  440  are connected between the drain and the gate of the FET  424  to keep the FET  424  biased in a manner to allow the FET  424  to conduct current between the battery cells  305  and the low-power terminal  220 . The gate of the FET  424  is modulated by the voltage regulator  432 . 
     The voltage divider circuit  428  is connected between the low-power terminal  220  and the ground terminal  210 . The voltage divider circuit  428  includes resistors  444 ,  448 ,  452 ,  456 , and  460 . The resistance values of the resistors  444 - 460  may be selected based on the desired references voltage that may be provided to the voltage regulator  432 . In one example, the voltage regulator  432  may be a micro-power voltage regulator including a bipolar junction transistor and a Zener diode reference optimized for μA level bias currents.  FIG. 5  is a simplified block diagram of the voltage regulator  432  illustrating the pin connections of the bipolar junction transistor  505  and the Zener diode  510 . 
     Returning to  FIG. 4 , the emitter of the bipolar junction transistor  505  is connected to the cathode of the Zener diode  510 . As a result, the base-emitter junction of the bipolar junction transistor  505  is in series with the Zener diode  510 . The anode of the Zener diode  510  is connected to ground. The collector of the bipolar junction transistor  505  is connected to the gate of the FET  424 . The base of the bipolar junction transistor  505  receives the reference voltage from the voltage divider circuit  428 . 
     The voltage loop  404  operates to keep the voltage constant at the low-power terminal  220 . The collector current of the bipolar junction transistor  505  varies proportionally to the voltage presented at the base terminal of the bipolar junction transistor  505 . When the load at the low-power terminal  220  is increased, the voltage across the voltage divider circuit  428  decreases. As a result, the reference voltage provided to the voltage regulator  432  decreases, which, in turn, reduces the collector current. The collector current is also the current through the pull up resistors  436 ,  440 . As such, the gate-source voltage of the FET  424  increases, which then conducts more current and increases the voltage provided at the low-power terminal  220 , which is also the voltage across the voltage divider circuit  428 . A stabilizer circuit  464  may be used to form a compensation network to stabilize the voltage loop  404 . 
     The current loop  408  maintains operation of the low-current supply circuit  400  in the event of excess current or a short circuit condition. The current loop  408  may be designed to have a foldback feature which allows a first load current (e.g., 100 mA) for a pre-defined timed period before reducing the current output to a constant second load current (e.g., 50 mA). The current loop  408  includes a current regulator circuit  468 , a current sensor  472  (e.g., a current sense resistor), and a timer circuit  476 . 
     The current regulator circuit  468  includes a first bipolar junction transistor  480  and a second bipolar junction transistor  484 . The first bipolar junction transistor  480  modulates the gate voltage of the FET  424  until the current sensor  472  indicates that the low-power circuit  320  is outputting a first load current. The timer circuit  476  including a resistor and a capacitor is connected between the base and emitter of the second bipolar junction transistor  484 . The resistance and capacitance values of the timer circuit  476  may be selected based on the desired timing before which the load current drops from the first load current to the second load current. 
     Approximately at the same time the first bipolar junction transistor  480  is modulating the FET  424 , the capacitor of the timer circuit  476  is being charged. For example, the capacitor and resistor values of the timer circuit  476  may be selected such that the capacitor of the timer circuit  476  charges in 1 s. When the capacitor of the timer circuit  476  is charged, the second bipolar junction transistor  484  starts conducting current thereby producing a voltage drop across the second bipolar junction transistor  484 . The first bipolar junction transistor  480  then modulates the FET  424  until the current output reaches the second load current (e.g., 50 mA). 
       FIG. 6  is a simplified circuit diagram of another embodiment of a low-current supply circuit  600  of the low-power circuit  320 . The low-current supply circuit  600  may function in a manner similar to the low-current supply circuit  400 . The low-current supply circuit  600  includes a voltage loop  604  and a current loop  608  within the voltage loop  604 . The low-current supply circuit  600  receives input power from the battery cells  305  over a positive terminal  612  and a negative terminal  616 . The nominal voltage range of the input power received over the terminals  612  and  616  may be between, for example, 40 Volts (V) to 80 V. 
     A fuse  620  is connected to the positive terminal  612  to act as a circuit breaker when an excess current flows through the low-current supply circuit  600 . The fuse  620  may be rated for a current higher than a current output of the low-current supply circuit  600  to allow the low-current supply circuit  600  to momentarily allow higher current without nuisance tripping. In one example, the fuse  620  may be rated for 200 mA at 125 V to allow an output current of 100 mA without nuisance tripping of the fuse  620 . 
     The voltage loop  604  includes a field-effect-transistor (FET)  624 , a voltage divider circuit  628 , and a voltage regulator  632 . The FET  624  is connected between the battery cells  305  and the low-power terminal  220 . In the illustrated embodiment, a drain of the FET  624  is connected to the output of the fuse  620 , and the source of the FET  624  is connected to the low-power terminal  220 . Pull up resistors  636  and  640  are connected between the drain and the gate of the FET  624  to keep the FET  624  biased in a manner to allow the FET  624  to conduct current between the battery cells  305  and the low-power terminal  220 . The gate of the FET  624  is modulated by the voltage regulator  632 . 
     The voltage divider circuit  628  is connected between the low-power terminal  220  and the ground terminal  210 . The voltage divider circuit  628  includes resistors  644 ,  648 ,  652 , and  656 . The resistance values of the resistors  644 - 656  may be selected based on the desired reference voltages that may be provided to the voltage regulator  632 . As described above, the voltage regulator  632  may be a micro-power voltage regulator including a bipolar junction transistor and a Zener diode reference optimized for μA level bias currents (for example, as shown in  FIG. 5 ). 
     The emitter of the bipolar junction transistor  505  is connected to the cathode of the Zener diode  510 . As a result, the base-emitter junction of the bipolar junction transistor  505  is in series with the Zener diode  510 . The anode of the Zener diode  510  is connected to ground. The collector of the bipolar junction transistor  505  is connected to the gate of the FET  624 . The base of the bipolar junction transistor  505  receives the reference voltage from the voltage divider circuit  628 . 
     The voltage loop  604  operates to keep the voltage constant at the low-power terminal  220 . The collector current of the bipolar junction transistor  505  varies proportionally to the voltage presented at the base terminal of the bipolar junction transistor  505 . When the load at the low-power terminal  220  is increased, the voltage across the voltage divider circuit  628  decreases. As a result, the reference voltage provided to the voltage regulator  632  decreases, which, in turn, reduces the collector current. The collector current is also the current through the pull up resistors  636 ,  640 . As such, the gate-source voltage of the FET  624  increases, which then conducts more current and increases the voltage provided at the low-power terminal  220 , which is also the voltage across the voltage divider circuit  628 . A stabilizer circuit  664  may be used to form a compensation network to stabilize the voltage loop  604 . 
     The current loop  608  protects the low-current supply circuit  600  in the event of excess current or a short circuit condition. The current loop  608  may be designed to have a fold-back feature which allows a first load current (e.g., 180 mA) for a pre-defined time period (e.g., time) before reducing the current output to a constant second load current (e.g., 60 mA). The current loop  608  includes a current regulator circuit  668 , a current sensor  672  (e.g., current sense resistors), and a timer circuit including a resistor  676  and a capacitor  680 . 
     The current regulator circuit  668  includes a first bipolar junction transistor  688  and a second bipolar junction transistor  684 . The first bipolar junction transistor  688  modulates the gate voltage of the FET  624  until the current sensor  672  indicates that the low-current supply circuit  600  is outputting a first load current. The timer circuit, including a resistor  676  and a capacitor  680 , is connected between the base and emitter of the second bipolar junction transistor  684 . The resistance and capacitance values of the timer circuit may be selected based on the desired timing before which the load current drops from the first load current to the second load current. 
     Approximately at the same time the first bipolar junction transistor  688  is modulating the FET  624 , the capacitor  680  of the timer circuit  676  is being charged. For example, the capacitor  680  and resistor  676  values of the timer circuit may be selected such that the capacitor  680  of the timer circuit charges in 700 ms. When the capacitor  680  of the timer circuit is charged, the second bipolar junction transistor  684  starts conducting current thereby producing a voltage drop across the first bipolar junction transistor  687 . The second bipolar junction transistor  684  then modulates the FET  624  until the current output reaches the second load current (e.g., 60 mA). 
       FIG. 7  is a simplified circuit diagram of one embodiment of a high-current supply circuit  700  of the low-power circuit  320 . In the example illustrated, the high-current supply circuit  700  includes a fuse  704  an input switch  708 , an enable switch  712 , a flyback converter  716 , a startup circuit  720 , a clamp circuit  724 , a primary switch  728 , and a transformer circuit  732 . The fuse  704  protects the high-current supply circuit  700  from short-circuit faults. The fuse  704  may have a nominal rating of, for example, 500 mA. The fuse  704  may be dimensioned to allow for full power operation at low line input. 
     When an enable input  736 , for example, a wake-up signal, is applied to the enable switch  712 , the enable switch  712  closes the input switch  708 , thereby allowing current from the battery cells  305  to flow to the high-current supply circuit  700 . The startup circuit  720  provides an initial power supply to operate the converter  716 . 
       FIG. 8  illustrates one example embodiment of the startup circuit  720 . In the example illustrated, the startup circuit  720  includes a first resistor  804 , a second resistor  808 , a third resistor  812 , a switch  816 , a capacitor  820 , and a diode  824 . The first resistor  804 , the switch  816  and the capacitor  820  are connected in series between the positive power supply  828  and ground  832 . The second resistor  808 , the third resistor  812  and the diode  824  are connected in series between the positive power supply  828  and ground  832  and in parallel to the first resistor  804 , the switch  816 , and the capacitor  820 . 
     Initially, the voltage across the capacitor  820  may be zero. The second resistor  808 , the third resistor  812 , and the diode form, for example, 15V reference on a gate of the switch  816 . As power is applied to the startup circuit, the switch  816  is turned on. The capacitor  820  is then charged up and by the drain current of the switch  816 . When the voltage across the capacitor  820  is, for example, approximately 8V, the startup circuit  720  powers the converter  716 . 
     Returning to  FIG. 7 , when the converter  716  receives the startup power, the converter  716  starts switching and modulating a gate of the primary switch  728 . Eventually, the converter  716  starts up and regulates to, for example, approximately 15V. At this point, the startup circuit  720  may be turned off and the converter  716  may be powered by the output of the high-current supply circuit  700 . 
     The clamp circuit  724  manages energy in the leakage inductance of the transformer circuit  732 . The transformer circuit  732  includes a primary winding  740 , and three secondary windings  744 ,  748 , and  752 . When the primary switch  728  is closed, the voltage drawn across the primary winding  740  is stepped down and provided to the secondary windings  744 ,  748 , and  752 . The secondary winding  744  provides the low-power voltage supply at the low-power voltage supply terminal  220 . The secondary windings  748  and  752  provide power to the discharging switch  335  and the charging switch  340  of the battery pack  100 . In some embodiments, a low dropout regulator (LDO) may be used instead of the transformer circuit  732  to step down the voltage. 
     When there is an activity that enables the high-current supply circuit  700  of the low-power circuit  320 , the high-current supply circuit  700  may remain enabled, for example, for 100 ms from last known activity before disabling the high-current supply circuit  700  and enabling the low-current supply circuit  600 . This may, for example, allow the battery pack  100  sufficient time for an orderly shutdown, to attempt a communications restart in the event of a fault. 
     With reference to  FIG. 9 , a device terminal block  900  includes a positive power terminal  905 , a ground terminal  910 , a low-power terminal  920 , a positive transmission terminal  925 , a negative transmission terminal  930 , a positive receiver terminal  935 , and a negative receiver terminal  940 . As described above, the positive power terminal  905  and the ground terminal  910  are connected to power terminals (i.e., positive battery terminal  205  and ground terminal  210 ) of the battery pack  100  to receive a main discharging current for the operation of the electrical device. The low-power terminal  920  receives a low-power voltage supply from the low-power terminal  220  of the battery pack  100  to power certain functions of the electrical device. 
     The positive transmission terminal  925 , the negative transmission terminal  930 , the positive receiver terminal  935 , the negative receiver terminal  940  may together be referred to as “communication terminals” of the electrical device. The communication terminals allow for differential communication between the battery pack  100  and the electrical device. As with the communication terminals of the battery pack  100 , the illustrated device communication terminals are only used to either receive or transmit data but not both. In other embodiments, the device communication terminals follow a full-duplex standard (for example, RS485 standard). 
       FIG. 10  is a simplified block diagram of an electrical device  1000 . The electrical device  1000  includes a device controller  1010 , a device memory  1015 , a load (e.g., a motor  1020 ), a load (motor) controller  1025 , and a device transceiver  1030 . The motor  1020  may be a brushed or brushless motor and is controlled by the motor controller  1025 . 
     The motor controller  1025  may be a switch bridge including FETs that control the operation of the motor  1020 . The motor controller  1025  may also include position sensors and other motor sensors. The motor controller  1025  may send positional information of the motor  1020  to the device controller  1010  and may receive control signals from the device controller  1010 . 
     The device controller  1010  may be implemented in various ways including ways similar to those described above with respect to the battery controller  310 . Likewise, the device memory  1015  may be implemented in various ways including ways that are similar to those described with respect to the battery memory  315 . The device memory  1015  may store instructions received and executed by the device controller  1010  to carry out the functionality. The device controller  1010  receives operating power from the low-power terminal  920 . In some embodiments, the device controller  1010  and the battery pack controller  310  may be implemented on a single controller. 
     In some embodiments, a discharging switch  1035  is connected between the positive power terminal  1005  and the motor controller  1025 . The device controller  1010  operates to control (e.g., opens and closes) the discharging switch  1035  to control the discharge from the battery pack  100 . The discharging switch  1035  may be implemented using bi-polar junction transistors, field-effect-transistors (FETs), etc. In some embodiments, the discharging switch  1035  may be connected on the ground-side of the motor controller  1025  between the motor controller  1025  and the ground terminal  910 . 
     In the illustrated example, the device transceiver  1030  is implemented as a differential communication transceiver (e.g., Texas Instruments SN65HVD7 Full Duplex RS-485 Transceiver). The device transceiver  1030  receives a transmission signal  1040  from the device controller  1010  and sends a receiver signal  1045  to the device controller  1010 . The device transceiver  1030  is also connected to the communication terminals. 
     When the electrical device  1000  transmits a communication signal to a connected battery pack  100 , the device controller  1010  sends the transmission signal  1040  in addition to a transmission enable signal  1050  to the device transceiver  1030 . When the device transceiver  1030  receives the transmission enable signal  1050 , the device transceiver  1030  converts the transmission signal  1040  to complementary transmission signals at the positive transmission terminal  925  and the negative transmission terminal  930 . 
     When the device transceiver  1030  receives a receiver enable signal  1055  from the device controller  1010 , the device transceiver  1030  receives complementary signals from the positive receiver terminal  935  and the negative receiver terminal  940 , converts the complementary signals to a single receiver signal  1045 , and sends the receiver signal  1045  to the device controller  1010 . 
     In other embodiments, rather than the device transceiver  1030 , the device  1000  may include separate transmitting and receiving components, for example, a transmitter and a receiver. 
     During a sleep state, the battery pack  100  may disable the receiver terminals  235  and  240  by sending a receiver disable signal  360 . In some embodiments, the device transceiver  1030  may send a wake-up pulse to the battery pack  100  to request operational power for the electrical device  1000 . The battery pack  100  may include a wake-up circuit to detect the wakeup pulse, which, in turn, will drive an interrupt to the battery controller  310 . The battery controller  310  enables the receiver functions of the battery transceiver  330  upon receiving the interrupt. 
     With reference to  FIG. 11 , a charger terminal block  1100  includes a ground terminal  1110 , a charger terminal  1115 , a positive transmission terminal  1125 , a negative transmission terminal  1130 , a positive receiver terminal  1135 , and a negative receiver terminal  1140 . The charger terminal  1115  and the ground terminal  1110  are connected to terminals (e.g., the charger terminal  215  and ground terminal  210 ) of the battery pack  100  to charge the battery cells  305  of the battery pack  100 . A low-power terminal may not be needed, because the charger independently receives operating power from an external power source. 
     The positive transmission terminal  1125 , the negative transmission terminal  1130 , the positive receiver terminal  1135 , the negative receiver terminal  1140  may together be referred to as “communication terminals” of the charger. The communication terminals allow for differential communication between the battery pack  100  and the charger. As with the communication terminals of the battery pack  100  and the electrical device  1000 , the illustrated charger communication terminals are only used to either receive or transmit data but not both. In other embodiments, the charger communication terminals follow a full-duplex standard (for example, RS485 standard). 
       FIG. 12  is a simplified block diagram of a charger  1200 . The charger  1200  includes a charger controller  1210 , a charger memory  1215 , a power converter  1220 , a power source connector  1225 , and a charger transceiver  1230 . The power source connector  1225  connects to an external power source (e.g., wall outlet) to receive power for charging a battery pack  100 . The power converter  1220  converts the AC power received from the external power source to a DC power to charge the battery pack  100 . The power converter  1220  may receive control signals from the charger controller  1210  to control the charging operation. 
     The charger controller  1210  may be implemented in various ways including ways similar to those described above with respect to the battery controller  310 . Likewise, the charger memory  1215  may be implemented in various ways including ways similar to those described above with respect to the battery memory  315 . The charger memory  1215  may store instructions received and executed by the charger controller  1210  to carry out the functionality. The charger controller  1210  receives operating power from the power converter  1220 . 
     In some embodiments, a charging switch  1235  is connected between the charger terminal  1115  and the power converter  1220 . The charger controller  1210  controls (e.g., opens and closes) the charging switch  1235  to control charging of the battery pack  100 . The charging switch  1235  may be implemented using bi-polar junction transistors, field-effect-transistors (FETs), etc. In some embodiments, the charging switch  1235  may be connected on the ground-side of the power converter  1220  between the power converter  1220  and the ground terminal  1110 . The charger controller  1210  may monitor the positive power terminal  1205  to determine a state of charge of the battery pack  100 . In some embodiments, back-to-back MOSFETs may be used for the charging switch  1235 . MOSFETs include a body diode which allows a small amount of current to flow through even when the MOSFET is open (i.e., turned off). Connecting a second MOSFET back-to-back with a first MOSFET such that the body diodes are pointing in the opposite direction may ensure that no current flows through the charging terminal  1115  when the MOSFETs are open (i.e., turned off). 
     In the illustrated example, the charger transceiver  1230  is implemented as a differential communication transceiver (e.g., Texas Instruments SN65HVD7 Full Duplex RS-485 Transceiver). The charger transceiver  1230  receives a transmission signal  1240  from the charger controller  1210  and sends a receiver signal  1245  to the charger controller  1210 . The charger transceiver  1230  is also connected to the communication terminals. 
     When the charger  1200  transmits a communication signal to a connected battery pack  100 , the charger controller  1210  sends the transmission signal  1240  in addition to a transmission enable signal  1250  to the charger transceiver  1230 . When the charger transceiver  1230  receives the transmission enable signal  1250 , the charger transceiver  1230  converts the transmission signal  1240  to complementary transmission signals at the positive transmission terminal  1125  and the negative transmission terminal  1130 . 
     When the charger transceiver  1230  receives a receiver enable signal  1155  from the charger controller  1210 , the charger transceiver  1230  receives complementary signals from the positive receiver terminal  1135  and the negative receiver terminal  1140 , converts the complementary signals to a single receiver signal  1145 , and sends the receiver signal  1145  to the charger controller  1210 . 
     In other embodiments, rather than the charger transceiver  1230 , the charger  1200  may include separate transmitting and receiving components, for example, a transmitter and a receiver. 
     Whenever the battery pack  100  connects to an electrical device  1000  or a charger  1200  for the first time, a full authentication process may be done before the electrical device  1000  or the charger  1200  may be granted permission for deployment. A quick re-authentication feature enables a fast means for devices to re-engage after a sleep event without requiring a full authentication. 
     This quick re-authentication process starts after a successful full authentication, in which the device controller  1010  (or a charger controller  1210 ) generates a random number (or a series of random numbers) and shares those numbers with the battery pack  100 . These numbers are used as quick “keys” to re-authenticate after waking from sleep. If, after waking, the device controller  1010  loads one of those values into the quick authentication location, then the battery pack  100  considers itself authenticated to the electrical device  1000 . If an invalid value is loaded, then a full authentication is required. 
     To accomplish this, the battery pack  100  has a “QUICK AUTHENTICATION” memory location, as well as a “SET QUICK AUTHENTICATION” location. The SET QUICK AUTHENTICATION may be write-only and may only able to be written after the battery pack  100  considers itself authenticated to the electrical device  1000  (or the charger  1200 ). The battery pack  100  may no longer consider itself fully authenticated once the battery transceiver  330  is put to sleep; however, the quick authentication is available unless the battery pack  100  has explicitly been instructed to drop the authentication session. This may happen, for example, when the electrical device  1000  detects that the battery pack  100  is about to be ejected and thus requests the battery pack  100  to drop the session. 
     QUICK AUTHENTICATION may be write-only and may only able to be written once prior to requiring a full authentication. This may be one of the only memory locations that is writeable when the battery pack  100  is not in an authenticated state. After QUICK AUTHENTICATION is written (once only), the value in QUICK AUTHENTICATION is compared to the value in SET QUICK AUTHENTICATION. If they match, the battery pack  100  considers itself authenticated. If they do not match, then the battery pack  100  requires a full authentication prior to any other communications. This process is illustrated in  FIG. 13 . 
     In order to facilitate the power down process of the system, a latch engagement system may be incorporated into a latch interface. This engagement system may consist of a switch which will inform the device controller  1010  that the battery pack  100  is about to be removed from the electrical device  1000 . Thus, the electrical device  1000  may enact a shutdown procedure of its power path and inform the battery pack  100  of the same. 
     When the communication session between the battery pack  100  and the electrical device  1000  is terminated, the battery pack  100  drops the authenticated session, disables the battery transceiver  330 , and enables a wakeup circuit. The battery pack  100  may need a wake-up signal through the battery transceiver  330  and then re-authentication to once again begin a valid communications session. 
     When the latch of the electrical device  1000  is engaged with the battery pack  100 , the electrical device  1000  enters a discovery mode. In the discovery mode, the electrical device  1000  sends a wake up pulse and begins an authentication process. When the latch is not engaged, the electrical device  1000  enters a sleep mode, in which the electrical device  1000  may be woken up when the latch is engaged. 
     At a physical interface level (i.e., physical interface between a battery pack  100  and the charger  1200  or the electrical device  1000 ), a communications session timeout may be enforced. Because full duplex communications are permitted, there are separate timeout rules for both the transmitter and the receiver. In short, communications must occur at a rate of at least every 10 msec. If communications do not happen within 10 msec, then the physical interface may timeout the session. In order to allow multiple retries within 10 msec, the communications period may be set at 4 msec intervals. Thus, if a fault happens, at least one retry is permitted before the physical interface will timeout and fault the communications session. 
     A timing of both the transmitter and the receiver is illustrated in  FIGS. 14-15 . The table below is a further explanation of the timeout conditions. 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 Role 
                 Period 
                 Action 
                 Rationale 
               
               
                   
               
             
            
               
                 Transmitter 
                 4 msec 
                 Packet byte 
                 Normal comms occurring every period 
               
               
                   
                   
                 PI_ACK 
                 If receiving a packet that is longer than the 
               
               
                   
                   
                   
                 period, then transmit the PI_ACK to indicate the 
               
               
                   
                   
                   
                 session is still valid 
               
               
                   
                   
                 PI_ERROR 
                 If an error condition occurs at the PI level, relay 
               
               
                   
                   
                   
                 this generic information to the other device 
               
               
                 Receiver 
                 10 msec 
                 Drop 
                 If the receiver has not received 
               
               
                   
                   
                 communications 
                 A valid byte 
               
               
                   
                   
                 session 
                 A PI_ACK (as first byte) 
               
               
                   
                   
                   
                 A PI_ERROR (as first byte) 
               
               
                   
                   
                   
                 Assume the communications session is faulted 
               
               
                   
               
            
           
         
       
     
     Referring to  FIGS. 9 and 11 , a thickness of one or more male terminals of an electrical device or a battery charger can be selected to optimize weight, strength, and durability characteristics of the terminal(s). In some embodiments, the terminals have a thickness of between 0.8 millimeter (mm) and 1.2 mm. In one example, the terminals have a thickness of about 1 mm. 
     In some constructions, male terminals  1110 - 1140  are (see  FIGS. 9 and 11 ) generally flat plates, including opposite axially-extending faces connected by opposite axially-extending edges. Each terminal  1110 - 1140  extends from the housing to a free end. In some constructions (see  FIG. 16 ), terminals (including power terminals  905 ,  910 ) extend above the structure of the guide rails  1260 . 
     In some embodiments (see, e.g.,  FIGS. 16 and 18 ), the terminals  905 ,  910  may be constructed to increase the strength, durability, etc., to, for example, protect against damage during drops or during handling of the electrical devices. In one construction (see  FIG. 16 ), a terminal (e.g., the positive power terminal  905 , the ground terminal  910 , etc.) includes a wing (e.g., a positive terminal wing  1605 , a ground terminal wing  1610 , etc.). 
     The illustrated positive terminal wing  1605  is integrally formed with the positive power terminal  905  and includes a connecting portion  1615  and a ledge portion  1620 . In the illustrated construction, the ledge portion  1620  extends transverse (e.g., substantially perpendicular) to the positive power terminal  905  towards a first side edge of the device terminal block  900 . The connecting portion  1615  transitions (e.g., curves) between and connects the positive power terminal  905  and the ledge portion  1620 . 
     Similarly, the illustrated ground terminal wing  1610  is integrally formed with the ground terminal  910  and includes a connecting portion  1625  and a ledge portion  1630 . In the illustrated construction, the ledge portion  1630  extends transverse (e.g., substantially perpendicular) to the ground terminal  910  toward an opposite second side edge of the device terminal block  900 . The connecting portion  1625  transitions (e.g., curves) between and connects the ground terminal and the ledge portion  1630 . 
     The terminal wings  1605 ,  1610  may be provided such that they extend only part of the axial length (e.g., between about 25% and about 50% of the axial length) of the associated terminal  905 ,  910 , respectively. Only the part of the terminal  905 ,  910  extending beyond the associated terminal wing  1605 ,  1610  may be received in the female terminal of the battery pack terminal block  115  (see  FIGS. 19-20 ). The terminal wings  1605 ,  1610  do not interfere with electrical connection between the terminals of the electrical device and the battery pack. In other embodiments, the terminal wings  1605 ,  1610  may extend the full axial length of the associated terminal  905 ,  910  respectively. 
     Referring to  FIG. 17 , the battery pack housing  105  may be constructed to accommodate the terminal wing(s)  1605 ,  1610 . The housing  105  includes a positive power terminal opening  1705  and a ground terminal opening  1710  to receive the positive power terminal  905  and the ground terminal  910 , respectively. In the illustrated construction, the positive power terminal opening  1705  includes a wing-receiving portion  1715  shaped to receive the positive terminal wing  1605 . Similarly, the illustrated ground terminal opening  1710  includes a wing-receiving portion  1720  shaped to receive the ground terminal wing  1610 . The wing  1605 ,  1610  may engage a wall of the associated wing-receiving portion  1715 ,  1720  to, for example, transfer forces, limit relative movement between the battery pack and the electrical device, etc., during drops or during handling of the electrical devices. 
     A battery pack housing (not shown) which is not constructed to accommodate the winged terminals  905 ,  910  (e.g., without the wing-receiving portion  1710 ,  1720 ) may be prevented from electrically connecting with an electrical device or a charger including such winged terminals  905 ,  910 . The winged terminals  905 ,  910  may contribute to a lock-out feature to inhibit electrical connection of incompatible battery packs and electrical devices or chargers. 
     In some embodiments, additional structure (e.g., support ribs, dimples, etc., having different shapes, constructions) may be provided on the power terminal(s) instead of or in addition to the terminal wing(s)  1605 ,  1610 . Referring to  FIG. 18 , the positive power terminal  905  and the ground terminal  910  are provided with one or more support ribs  1805  on one face. The rib(s)  1805  provide additional support to each terminal  905 ,  910 . 
     In some embodiments (see  FIG. 18 ), the ribs  1805  are separate from and attached to the terminal(s)  910 . In such constructions, the ribs  1805  may be formed of a different material (e.g., plastic) than the terminal(s)  905 ,  910  (formed of metal). In some embodiments (see  FIGS. 24-26 ), the ribs  1805  are integrally formed with the terminal(s)  905 ,  910  and of the same material (e.g., metal). 
     With multiple support ribs  1805 , the ribs  1805  are spaced apart (e.g., substantially equidistant) along the face of the terminal  905 ,  910 . The ribs  1805  may be provided such that they extend only part of the axial length (e.g., between about 25% and about 50% the axial length (e.g., about 33%)) of the associated terminal  905 ,  910 . Only the part of the terminal  905 ,  910  extending beyond the ribs  1805  is received in the female terminals of the battery pack terminal block  115  (see  FIGS. 19-20 ). The ribs  1805  do not inhibit electrical connection between the terminals of the electrical device and the battery pack. In other embodiments, the ribs  1805  may extend the full axial length of the associated terminal  905 ,  910 . 
     Referring to  FIGS. 19-20 , the battery pack housing  105  is constructed to accommodate the terminal(s)  905 ,  910  with the rib(s)  1805 . Particularly, the width of the positive power terminal opening  1705  and the ground terminal opening  1710  is increased to accommodate the ribs  1805 . 
     A battery pack housing (not shown) which is not constructed to accommodate the terminal(s)  905 ,  910  with rib(s)  1805  (e.g., without the increased width terminal opening(s)  1705 ,  1710 ) may be prevented from electrically connecting with an electrical device or a charger including such terminals  905 ,  910 . The terminal(s)  905 ,  910  with rib(s)  1805  may contribute to a lock-out feature to inhibit electrical connection of incompatible battery packs and electrical devices or chargers. 
     In some constructions (see  FIGS. 24-26 ), one or more terminal(s) (e.g., the terminals  905 ,  910 ) include wings  1605 ,  1610 , respectively, and ribs  1805 . The terminal wings  1605 ,  1610  may be provided such that they extend only part of the axial length (e.g., between about 75% and about 95% (e.g., about 91%) of the axial length) of the associated terminal  905 ,  910 , respectively. Likewise, the ribs  1805  may be provided such that they extend only part of the axial length (e.g., between about 25% and about 50% the axial length (e.g., about 33%)) of the associated terminal  905 ,  910 . As shown, the length of the wings  1605 ,  1610  and the ribs may be different. In other embodiments, the terminal wings  1605 ,  1610  and the ribs  1805  may extend the full axial length of the associated terminal  905 ,  910  respectively. 
     In the illustrated construction, each wing  1605 ,  1610  is formed with the associated terminal  905 ,  910 . The illustrated ribs  1805  are also formed with the associated terminal  905 ,  910 , for example, by stamping, such that the opposite face of the terminal  905 ,  910  has corresponding recesses  1810 . 
     It should be understood that, in other constructions (not shown), the battery pack may include male terminals and the electrical device and the charger may include female terminals. In such constructions (not shown), the pack male terminal(s) may include the wing(s) and/or the support rib(s), and the device housing or the charger housing may include the terminal opening to accommodate the wing(s), the rib(s), etc. 
     In some embodiments, additional support structures are added to the device housing and the battery pack housing  105 .  FIGS. 21-22  illustrate a device housing  2105  including a terminal block portion  2110 . The terminal block portion  2110  includes ribs  2115  positioned outside each side surface of the device terminal block  900 . 
     Referring to  FIG. 17 , the pack housing  105  is constructed to accommodate the ribs  2115 . Cutouts  2120  in the pack housing  105  receive the ribs  2115  when the battery pack is attached to the electrical device. 
       FIG. 23  illustrates another embodiment of a device housing  2305  including a terminal block portion  2310 . The device housing  2305  includes side surface ribs  2315  on either side (that is, a first side and a second side) of the housing  2305 . Support ribs  2320  are positioned on either side of the terminal block portion  2310 . The illustrated support ribs  2320  are provided on an inside portion compared to the side surface ribs  2315  on the device housing  2305 . 
     Additional connection ribs  2325  are positioned between the support ribs  2320  and the side surface ribs  2315 . The connection ribs  2325  connect the support ribs  2320  to the side surface ribs  2315  to support the support ribs  2320 . The rib arrangement including the side surface ribs  2315 , the support ribs  2320 , and the connection ribs  2325  provide additional support to the terminal block portion  2310  to, for example, protect against damage during drops or during handling of the electrical devices. 
     Thus, the invention may provide, among other things, a battery pack terminal configuration. The configuration may include a low-power terminal and/or a row of one or more communication terminals spaced from a row of power terminals. The invention may provide a battery pack including a low power circuit operable to provide a reduced voltage from all of the battery cells of the battery pack to the powered electrical device. The invention may provide a terminal (e.g., a male blade terminal) with terminal support structure (e.g., a wing, one or more ribs, etc.). 
     One or more independent features and/or independent advantages of the invention may be set forth in the claims.