Patent Publication Number: US-9431837-B2

Title: Integrated battery management system and method

Description:
BACKGROUND 
     The invention relates generally to battery devices and systems and, more particularly, to a vehicle battery management system. 
     Batteries composed of one or more electrochemical cells capable of converting chemical energy into a more readily usable form of electrical energy are widely employed in many industries and applications. For example, many such batteries are starting, lighting, and ignition (SLI) batteries capable of starting the internal combustion engines of motorcycles, cars, trucks, and other vehicles. Batteries of this type can typically be discharged and replenished with charge in multiple cycles before the life cycle of the battery is depleted. Typically, when an end user purchases a new battery, for example, for integration into a vehicle, such as a motorcycle, the charge level of the battery is unknown. Unfortunately, upon insertion into the user&#39;s vehicle, the battery may not function if the charge level of the battery has been depleted, for example, during the time the battery was on a display shelf before purchase. Additionally, charging of such batteries typically requires connection of lead cables to the battery terminals, which can be cumbersome and time consuming. Accordingly, there exists a need for battery systems that overcome these drawbacks of traditional systems. 
     SUMMARY 
     The present disclosure relates to a battery system including a housing and a plurality of battery cells disposed in the housing. The battery system also includes a battery management system disposed in the housing. The battery management system is configured to monitor one or more operational parameters of the battery system. The battery management system is electrically coupled to a positive terminal and a negative terminal of the battery system. Additionally, the battery system includes a multi-conductor connector disposed in an outer surface of the housing. The multi-conductor connector is electrically coupled to the battery management system. Additionally, the battery system includes a state of charge indicator configured to provide an indication of a state of charge of the battery system. The state of charge indicator includes a first multi-conductor connector configured to couple to the multi-conductor connector of the battery module. 
     The present disclosure also relates to a battery system including a housing and a multi-conductor connector disposed in an outer surface of the housing. The battery system also includes a charging/maintaining device configured to charge the battery system. Further, the battery system includes a state of charge indicator configured to provide an indication of a state of charge of the battery system. The state of charge indicator includes a first connector configured to couple to the multi-conductor connector of the battery system and a second connector configured to couple to the charging/maintaining device. The second connector includes a pair of electrical contracts configured to receive charging power from the charging/maintaining device. Additionally, the first connector includes a pair of electrical contacts configured to transmit the charging power to the multi-pin connector of the battery system. 
     The present disclosure further relates to battery system including a housing and a plurality of battery cells disposed in the housing. The battery system also includes a battery management system disposed in the housing and configured to monitor one or more operational parameters of the battery system. The battery management system includes a memory configured to store operational parameter history information, usage information, or a combination thereof. The battery system also includes a multi-conductor connector disposed in an outer surface of the housing and electrically coupled to the battery management system. Additionally, the battery system includes a state of charge indicator configured to provide an indication of a state of charge of the battery system. Further, the battery system includes a data input/output tool configured to download information to the memory of the battery system, read information stored in the memory of the battery system, or a combination thereof. The state of charge indicator and the data input/output tool are configured to be interchangeably coupled to the multi-conductor connector of the battery system. 
    
    
     
       DRAWINGS 
         FIG. 1  is a perspective view of  FIG. 1  is perspective view of an embodiment of a vehicle having a battery module and showing attachment of the battery to a state of charge indicator coupled to a battery charger or maintainer; 
         FIG. 2  is a perspective view of an embodiment of a motorcycle having a battery module coupled to a state of charge indicator that may be coupled to a battery charger or maintainer; 
         FIG. 3  is a schematic diagram of an embodiment of a state of charge indicator and a battery including a battery management system; 
         FIG. 4  is a block diagram of an embodiment of the battery of  FIG. 3  including the battery management system; 
         FIG. 5  is a partial exploded view of an embodiment of the battery of  FIG. 3  including the battery management system; 
         FIG. 6  is a perspective view of an embodiment of the state of charge indicator of  FIG. 3 ; 
         FIG. 7  is a flow chart representing logic of a sleep mode regime adapted to transition the battery of  FIG. 3  into a sleep mode; and 
         FIG. 8  is a flow chart representing logic of a wake-up regime adapted to transition the battery of  FIG. 3  from a sleep mode to an operational mode. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     As described in more detail below, present embodiments are directed towards systems and methods for battery monitoring and management. Systems and methods may include a battery management system including one or more sensors and processing circuitry. The battery management system may monitor parameters of the battery, such as voltage, temperature, current, and state of charge. Additionally, the battery management system may protect the battery by performing cell balancing. Furthermore, the battery management system may protect the battery by preventing over-discharge (e.g., under-voltage) of the battery and/or of individual cells of the battery, input over-voltage, input over-current, and over-heating by monitoring operational parameters of the battery and placing the battery into a sleep mode in response to detected undesirable operating conditions. The battery management system may include a connector adapted to couple a state of charge indicator to the battery management system so that the state of charge indicator may provide an indication of the state of charge of the battery. As such, the state of charge indicator may be tethered to the battery via the connector. The state of charge indicator may also interface between the battery management system and a charging system. In some embodiments, the state of charge indicator may include a reset button (e.g., momentary contact switch) adapted to allow for manually placing the battery into a sleep mode and manually reactivating the battery (i.e., “waking” from sleep mode). 
     With the foregoing in mind,  FIG. 1  illustrates a battery system  10  including a battery  12  disposed in a vehicle  14 . The battery  12  may typically be used in a vehicle, as shown, which may be a car, truck, boat, motorcycle, recreational vehicle, golf cart, four wheeler, offroad vehicle, power sports vehicle, power water craft, or other vehicle that uses battery power. While the battery  12  is illustrated as being positioned in the trunk or rear of the vehicle  14 , the location of the battery  12  may differ in other embodiments. For example, the position of the battery  12  may be selected based on the available space within the vehicle, the desired weight balance of the vehicle, the location of other components used with the battery system  10  (e.g., cooling devices, etc.), and a variety of other considerations. In some contexts and embodiments, the battery may be somewhat difficult to access, and aspects of the present disclosure allow for checking the state of charge of the battery, charging the battery, controlling sleep mode and other operations of the battery, and so forth, while the battery is still installed, greatly facilitating these operations when such access is difficult. 
     The battery  12  may be a starting, lighting, and ignition (SLI) battery of any desired design, type, voltage, and capacity, or the battery  12  may be a deep cycle battery, depending on the vehicle type and the application. Moreover, the battery may be designed and constructed in accordance with any currently known or later developed technology, such as wet cell technologies, glass mat technologies, gel cell technologies, etc. In some embodiments, the battery  12  may be a lithium-ion battery. Further, in some embodiments, the battery  12  may be a summer-only battery and may not be adapted for use during the winter. Similarly, when the vehicle is only used sporadically or seasonally, the techniques described allow for management of the battery charge and functions to accommodate such selected use. 
     The battery  12  includes positive and negative terminals  16 , which may be coupled to a wiring harness or other components within the vehicle  14  that utilize the voltage output of the battery  12 . Present embodiments of the battery  12  may also include a connector  18  (e.g., a multi-conductor connector), such as a female plug, to couple external electrical conductors to internal components of the battery  12 . For example, as illustrated, the connector  18  may couple a state of charge indicator  20  to the battery  12  via a lead  22  of the state of charge indicator  20  disposed in the connector  18 . As will be described in more detail below, the state of charge indicator  20  may receive data from the battery  12 , such as the voltage of the battery  12 , and may provide an indication of the state of charge of the battery  12 . Additionally, the state of charge indicator  20  may be adapted to couple to a battery charger/maintainer  24  with a lead  26 . 
     Once the state of charge indicator  20  is electrically coupled to the charger/maintainer  24 , electrical charging power may be applied through the lead  26 , the state of charge indicator  20 , the lead  22 , and the connector  18 , in order, to build up a charge in the battery  12 . The battery charger/maintainer  24  may receive power from a power grid  28  or other power source, which provides AC power to the battery system  10 . It should be noted that the battery charger/maintainer  24  may be any desirable battery charger or battery maintainer configured for use with the battery  12 . Battery chargers typically provide a high charging current to the battery  12  in order to charge the battery  12  relatively quickly (e.g., overnight), while battery maintainers typically provide a lower current “trickle” flow of charging power to the battery  12 . As may be understood by one skilled in the art, the battery charger/maintainer  24  may be portable, or may have a fixed location. Moreover, the charger/maintainer may implement any desired charging regime, such as regimes based on sensed voltage, stage of charge, battery voltage and capacity, and so forth. 
     Similarly,  FIG. 2  illustrates a motorcycle  40  having the battery  12  attached to the state of charge indicator  20 . Because the battery  12  in the motorcycle  40  (or certain other vehicles  14 ) may be difficult to access for connecting equipment directly to the terminals  16 , providing the state of charge indicator  20  may be desirable. The state of charge indicator  20  may be internally coupled to the terminals  16  and the connector  18  of the battery  12  via the lead  22 . Thus, the state of charge indicator  20  allows the user to read the state of charge of the battery  12  and to charge or maintain the battery  12  without requiring any disassembly to reach the terminals  16 . Again, the power grid  28  may provide AC power to the battery system  10 . Such arrangements may facilitate connection of the battery  12  to the charger/maintainer  24  by simply plugging the charger/maintainer  24  into the state of charge indicator  20  when desired. 
     It should be noted that when reference is made in the present disclosure to connections to the battery terminals, in many implementations, the connection will actually be made internally within the battery. That is, such connections may be made to connectors, conductors, or at other points where the internal battery circuits extend to and from the actual external terminals. 
       FIG. 3  shows an embodiment of the battery system  10  including the battery  12 , which includes an integrated (e.g., self-contained) battery management system  50 . As illustrated, the battery  12  includes an array  52  of battery cells  54  electrically coupled to the battery management system  50 . In certain embodiments, the battery cells  54  may be lithium-ion cells, lithium-iron phosphate cells, lithium polymer cells, nickel-metal-hydride cells, or any other suitable type of electrochemical cells. Additionally, the battery cells  54  may have any suitable physical configurations, such as prismatic, oval, cylindrical, polygonal, etc. 
     In the illustrated embodiment, the battery cells  54  are connected in series via bus bars  55 . That is, each bus bar  55  is coupled between a positive terminal  56  of one battery cell  54  and a negative terminal  58  of an adjacent battery cell  54 . However, it should be appreciated that the battery cells  54  may be employed in alternative array configurations, such as in parallel or in any other suitable arrangements involving parallel and serial configurations. Further, while four battery cells  54  are illustrated within the array  52 , any suitable number of battery cells  54  may be utilized. 
     In some embodiments, multiple battery cells  54  may be grouped into modules, with multiple modules forming the array  52 . In such embodiments, a first bus bar may be electrically coupled to the positive terminal  56  of each battery cell  54  within a module, and a second bus bar may be electrically coupled to the negative terminal  58  of each battery cell  54  within the module. The bus bars, in turn, may be electrically coupled to the battery management system  50  and configured to transfer an electrical power signal from the battery cells  54  to the battery management system  50 . Multiple modules may be connected in series and/or parallel to form the array  52  and to provide a desired electrical power output to a starting, lighting, ignition component of the vehicle  14 , a vehicle propulsion system, or some other load. For example, in one embodiment, the battery system  10  may include two modules connected in parallel, and each module may include four battery cells  54  connected in series. Among other functions, the battery management system may be connected to the cells at points that allow for balancing of loads and draws from the cells or groups, as discussed below. 
     As noted above, the battery  12  also includes the integrated (e.g., self-contained) battery management system  50 . In certain embodiments, the battery management system  50  may include one or more integrated circuits or printed circuit boards including discrete components mounted and interconnected on the printed circuit board, and the battery management system  50  may operate using power received from the array  52  of battery cells  54  (e.g., via a regulated power supply). Additionally, the battery management system  50  may be disposed within a housing  60  of the battery  12 . In some embodiments, the battery management system  50  may be disposed under a cover  62  of the battery  12 . For example, the battery management system  50  may be mounted to or permanently affixed to an interior surface of the cover  62 . In other embodiments, the battery management system  50  may be disposed between the cover  62  and the array  52  of battery cells  54 . For example, as will be described in more detail below with respect to  FIG. 5 , the battery management system  50  may be mounted to or permanently affixed to a support structure (e.g., a board mount) located above the array  52  of battery cells  54  such that the battery monitoring system  50  is offset from the cover  62  and the array  52 . 
     As will be described in more detail below, the battery management system  50  may be adapted to monitor and provide feedback related to the health of the battery  12 . For example, the battery management system  50  may be adapted to monitor one or more operational parameters of the battery  12 , such as a voltage, temperature, or current. Additionally, the battery management system  50  may provide data relating to the one or more operational parameters of the battery  12 . For example, the battery management system  50  may provide data, such as the state of charge of the battery  12 , to the state of charge indicator  20  via the connector  18 . Additionally, the battery management system  50  may log events (e.g., an event where an operational parameter exceeds a threshold) and may provide data regarding the events to a data input/output tool. Furthermore, the battery management system  50  may perform cell balancing, which may increase the performance and life of the battery  12 . Additionally, the battery management system  50  may protect the battery cells  54  from damage by transitioning the battery  12  to a sleep mode in response to detection of adverse events. For example, as described in more detail below, the battery management system  50  may force the battery  12  into a sleep mode when a voltage or current of the battery  12  drops below a predetermined level or in response to a sleep signal received from the state of charge indicator  20 . 
     To enable the monitoring of the battery  12 , the battery management system  50  may be adapted to receive signals from cell measurement electronics that monitor one or more parameters of the battery cells  54  of the array  52 . For example, a measurement device  64  may be associated with each battery cell  54 , or group of battery cells  54 , in the array  52 , and may be adapted to output signals to the battery monitoring system  50 . As illustrated in  FIG. 3 , the measurement device  64  may be mounted to an exterior surface  66  of each battery cell  54 . In certain embodiments, the measurement device  64  may be one or more sensors (e.g., a thermocouple, a voltmeter, an ammeter, etc.). In other embodiments, the measurement device  64  may be a printed circuit board or an integrated circuit that includes one or more sensors (e.g., a thermocouple, a voltmeter, an ammeter, etc.). 
     While the illustrated embodiment includes a measurement device  64  mounted to the exterior surface  66  of each battery cell  54 , it should be noted that in other embodiments, the measurement devices  64  may be permanently affixed to the respective exterior surfaces  66 , mounted to or otherwise affixed to an interior surface of each battery cell  54 , or arranged in any other suitable arrangement. As illustrated, each measurement device  64  includes a first lead  68  coupled to the positive terminal  56  of a respective battery cell  54 , and second lead  70  coupled to the negative terminal  58  of the respective battery cell  54 . Thus, each measurement device  64  may be communicatively coupled to the battery monitoring system  50 . Furthermore, in other embodiments, the measurement devices  64  may be sensors disposed on the battery management system (e.g., sensors disposed on the printed circuit board of the battery management system  50 ), and the measurement devices  64  may include leads coupling each measurement device  64  to the terminals  56  and  58  of a respective battery cell  54 . Thus, the measurement devices  64  may be associated with a respective battery cell  54 , but not directly mounted to or affixed to the respective battery cell  54 . In some embodiments, the battery system  10  may include a combination of measurement devices  64  that are mounted to battery cells  54  and measurement devices  64  that are disposed on the battery management system  50  and adapted to monitor operational parameters of a respective battery cell  54  via leads coupled to the terminals  56  and  58  of the respective battery cell  54 . 
       FIG. 4  is a schematic diagram of an embodiment of the battery system  10  including the battery management system  50  and the measurement device  64 . As illustrated, the measurement device  64  may include a voltmeter  90  electrically coupled to the first lead  68  and the second lead  70 . Because the first lead  68  is electrically coupled to the positive terminal  56  and the second lead  70  is electrically coupled to the negative terminal  58 , the voltmeter  90  will measure the voltage across the battery cell  54 . In the illustrated embodiment, the voltmeter  90  is also electrically coupled to a microprocessor  92 . However, it should be noted while reference is made in the present discussion to a microprocessor, any suitable processing circuitry may be employed. The microprocessor  92  may receive a signal from the voltmeter  90 , compute the voltage based on the received signal, and transmit the computed voltage to the battery management system  50 . For example, in certain embodiments, the voltmeter  90  may output an analog signal proportional to the measured voltage. The microprocessor  92  may convert the analog signal into a digital signal and may determine the voltage based on the digital signal. However, it should be noted that in some embodiments, the measurement device  64  may not include the microprocessor  92  or processing circuitry. In such embodiments, the voltmeter  90  may output an analog signal to the battery management system  50 , which may be adapted to determine the voltage using the received signal. In particular, the battery management system  50  may include a microprocessor  94 , or other suitable processing circuitry, which may be configured to receive a signal from the voltmeter  90  and determine the voltage based on the received signal. 
     As illustrated, the measurement device  64  may also include a thermocouple  96 . The thermocouple  96  may be communicatively coupled to the microprocessor  92 , if present, and to the microprocessor  94  of the battery management system  50 . Because the measurement device  64  may be in direct contact with an interior surface or exterior surface of the battery cell  54 , the thermocouple will output a signal indicative of the battery cell temperature. Accordingly, the microprocessor  92  and/or the microprocessor  94  may determine the cell temperature based on the signal. For example, in certain embodiments, the thermocouple  96  may output an analog signal proportional to the measured temperature. In such embodiments, the microprocessor  92  and/or the microprocessor  94  may be configured to convert the analog signal into a digital signal, and to determine the temperature based on the digital signal. 
     Additionally, the measurement device  64  may include an ammeter  98 . The ammeter  98  may be communicatively coupled to the microprocessor  92 , if present, and to the microprocessor  94  of the battery management system  50 . Accordingly, the microprocessor  92  and/or the microprocessor  94  may determine the current of the battery cell  54  based on the signal. For example, in certain embodiments, the ammeter  98  may output an analog signal proportional to the measured current. In such embodiments, the microprocessor  92  and/or the microprocessor  94  may be configured to convert the analog signal into a digital signal, and to determine the current based on the digital signal. 
     While the illustrated embodiment of the measurement device  64  includes the voltmeter  90 , the thermocouple  96 , and the ammeter  98 , it should be noted that alternative embodiments may include additional sensors configured to monitor other operational parameters of the battery cell  54 . For example, in certain embodiments, the measurement device  54  may include a sensor adapted to measure the specific gravity or pH level of an electrolyte within the battery cell  54 , which may be used to in the determination of the state of charge of the battery  12 . In further embodiments, the measurement device  64  may include a pressure sensor configured to detect a pressure within the battery cell  54 , an ohmmeter, or any other suitable sensor configured to monitor an electrical, physical or chemical parameter of the battery cell  54 . Furthermore, in certain embodiments, the measurement device  64  may also include a memory communicatively coupled to the microprocessor  90 , which may store information related to the battery cell  54  and/or algorithms to be used by the microprocessor  90  for the calculation of the various operational parameters. 
     Furthermore, in certain embodiments, the battery management system  50  may include one or more sensors adapted to measure operational parameters of the array  52  of the battery cells  54 . As illustrated, the battery management system  50  may include a voltmeter  100  and ammeter  102  that are communicatively coupled to the microprocessor  94  and are adapted to measure the total voltage and current, respectively, of the array  52 . Additionally, the battery management system  50  may include a thermocouple  104  communicatively coupled to the microprocessor  94  that is adapted to measure the temperature of one or more battery cells  54  of the array  52 . Further, it should be noted that the battery  12  may include any suitable sensor configured to monitor an electrical, physical or chemical parameter of the battery  12 . For example, in some embodiments, the battery  12  may include an additional voltmeter and ammeter adapted to measure an input voltage and current, respectively, transmitted from the charger/maintainer  24  to the battery  12 . 
     While reference is made here to certain sensors in the form of “meters”, it should be borne in mind that the actual sensors utilized may or may not include some sort of readout, as with conventional “meters”. That is, the “meters” (sensors) may be completely internal to the battery and management system. 
     The microprocessor  94  may be configured to calculate one or more operational parameters of the battery cells  54  and/or the battery  12 . For example, as noted above, the microprocessor  94  may receive signals from the voltmeter  90 , the thermocouple  96 , and the ammeter  98  and may calculate parameters such as the voltage, temperature, and current of the battery cell  54  based on the received signals. Additionally, the microprocessor  94  may calculate the voltage, current, and temperature of the battery  12  based on signals from the voltmeter  100 , ammeter  102 , and thermocouple  104 , respectively. For example, the microprocessor  94  may calculate a voltage and current of the power flowing from the battery cells  54  to the terminals  16  of the battery  12  based on signals received from one or more voltmeters  100  and ammeters  102  disposed on the battery management system  50 . In some embodiments, the battery management system  50  is configured to detect and calculate a voltage difference across each individual battery cell  54 , and across the entire array  52  of the battery cells  54 . This may enable the battery management system  50  to perform cell balancing as desired. 
     The battery management system  50  may include a memory  106 , which may store instructions and/or algorithms for calculating the operational parameters of the battery cells  54  and the battery  12 . Furthermore, in certain embodiments, the memory  106  may store thresholds for the operational parameters, such as a maximum temperature of the battery  12 , a maximum temperature of a battery cell  54 , a minimum voltage, current, and/or state of charge of the battery  12 , and a minimum voltage, current, and/or state of charge of a battery cell  54 . Accordingly, the microprocessor  94  may be configured to access the memory  106  to read the data stored in the memory  106 . 
     Further, the microprocessor  94  may be configured to calculate the state of charge of the battery  12 . The microprocessor  94  may be configured to calculate the state of charge of the battery  12  using any suitable signal or combinations of signals, such as signals from the voltmeter  90  for one or more battery cells  54 , from the voltmeter  100  of the battery management system  50 , from the ammeter  98  for one or more battery cells  54 , and/or from the ammeter  102  of the battery management system  50 . In certain embodiments, the microprocessor  94  may be configured to calculate the state of charge of the battery  12  based at least in part upon the voltage of the battery  12 , the discharge rate (e.g., discharge curve) of the battery  12 , and the temperature of the battery  12 . It should be noted that the voltage of the battery  12  may be determined using signals from the voltmeter  90  of one or more battery cells  54  and/or signals from one or more voltmeters  100  of the battery management system  50 . Similarly, the temperature of the battery  12  may be determined using signals from the thermocouple  96  of one or more battery cells  54  and/or signals from the thermocouple  104  of the battery management system  50 . Furthermore, it should be appreciated that the memory  106  may store information that may be accessed by the microprocessor  94  to facilitate the calculation of the state of charge, such as one or more algorithms and the discharge rate of the battery  12 . 
     The microprocessor  94  may communicate with the state of charge indicator  20  to provide an indication of the calculated state of charge of the battery  12 . As noted above, providing the state of charge indicator  20  as a tethered device may be desirable, because the state of charge may be easily assessed without requiring disassembly of the vehicle to access the battery  12 . Furthermore, in certain embodiments, the battery  12  may be difficult to access or reach in the vehicle (e.g., a motorcycle), and the tethered state of charge indicator  20  may be more easily accessible for the user than the battery  12 . 
     In some embodiments, the state of charge indicator  20  may be a visual indicator, such as one or more light emitting diodes (LED), that is illuminated in colors that correspond to the state of charge of the battery  12  (e.g., red indicates a discharged state, green indicates a charged state, and yellow indicates a partially charged state). For example, in certain embodiments, if the state of charge of the battery  12  is above a first threshold, the microprocessor  94  may send a signal to the state of charge indicator  20  that causes the state of charge indicator  20  to provide a first indication (e.g., a green LED). Additionally, if the state of charge of the battery  12  is below a second threshold, the microprocessor  94  may send a signal to the state of charge indicator  20  that causes the state of charge indicator to provide a second indication (e.g., a red LED). Further, in certain embodiments, if the state of charge of the battery  12  is between the first and the second threshold, the microprocessor  94  may send a signal to the state of charge indicator  20  that causes the state of charge indicator  20  to provide a third indication (e.g., a yellow LED). 
     In another embodiment, the state of charge indicator  20  may be a visual indication panel configured to display a percentage corresponding to the ratio of the current charge level to the total possible charge level that defines the battery&#39;s capacity. While the illustrated embodiment relates to the state of charge indicator  20 , it should be noted that any suitable type of output device (e.g., audio and/or visual output device) may be used to provide feedback to a user relating to the battery  12 . Furthermore, it should be noted that the feedback provided by the state of charge indicator  20 , or any other suitable output device, is not limited to the state of charge. For example, in other embodiments, an output device may provide feedback related to the temperature of the battery  12 , or some other desired parameter. 
     As noted above, the state of charge indicator  20  also interfaces between the battery  12  and the battery charger/maintainer  24 . Using the state of charge indicator  20  as an interface for coupling to the charger/maintainer  24  may be desirable because the user may more easily access the state of charge indicator  20  than the terminals  16  of the battery  12 . Generally, a battery charger may charge the battery  12  overnight, while a battery maintainer may charge the battery over a longer period of time, and/or simply maintain a desired state of charge. For example, a battery maintainer may be used to maintain the charge level of a battery of a power sports vehicle, which may discharge during periods of inactivity. The charger/maintainer  24  may include power conversion circuitry to convert or condition incoming power from the grid  26  in any way necessary to produce an output suitable for charging the battery  12 . Additionally, in certain embodiments, the charger/maintainer  24  may include charging control circuitry to monitor and control the delivery of charge to the battery  12 . In some embodiments, the charger/maintainer  24  may receive data, such as a state of charge of the battery  12 , from the battery management system  50  via the state of charge indicator  20 , and the charging control circuitry of the charger/maintainer  24  may use the received data to control the delivery of charge to the battery  12 . In other embodiments, the battery management system  50  may monitor the state of charge of the battery  12  and control the delivery of charge via start or stop signals sent to the charger/maintainer  24 . For example, the microprocessor  94  may be configured to send signals to the charger/maintainer  24  via the state of charge indicator  20  to initiate or stop the flow of charge based at least in part upon the state of charge of the battery  12 , the state of charge of one or more of the battery cells  54 , the voltage of the battery  12 , the voltage of one or more of the battery cells  54 , and/or any other suitable operational parameter. In one embodiment, the battery management system  50  may be configured to stop the flow of charge to the battery  12  in response to a determination that the state of charge of the battery  12  has reached a maximum state of charge threshold or the voltage of the battery  12  has reached a maximum voltage threshold. As such, the battery management system  50  may protect the battery cells  54  from overcharging. 
     The battery management system  50  may also protect the battery cells  54  from damage by monitoring operational parameters of the battery  12  and controlling the delivery of charge to the battery  12 . For example, the battery management system  50  may monitor the state of charge and/or voltage of each battery cell  54  of the battery  12  and control the delivery of charge to the battery  12  to facilitate cell balancing. The battery cells  54  may discharge at different rates, which may be intensified by higher battery cell temperatures. As a result, the battery cells  54  may be at different levels of charge (e.g. after a period of discharging or inactivity). While battery cells  54  in parallel may self balance to the lowest voltage, battery cells  54  in series may remain at different voltages. Thus, during charging, one or more battery cells  54  may reach a full state of charge earlier than other battery cells  54  in the array  52 . Overcharging the battery cells  54  that are fully charged may damage the battery cells  54 . Thus, it may be desirable to halt charging and balance the battery cells  54  before resuming charging. 
     Accordingly, the battery management system  50  may be configured to control a cell balancing system adapted to balance the battery cells  54 . The cell balancing system may be external or internal to the battery management system  50 . In certain embodiments, the battery management system  50  may apply a balancing algorithm to the battery cells  54 , which may select battery cells with the highest levels of charge (e.g., any battery cell with a state of charge or voltage greater than the battery cell with the lowest state of charge or voltage). The selected battery cells may be discharged by parallel resistors until the state of charge of the lowest charged battery cell is reached. Once the battery cells  54  are balanced, the battery management system  50  may send a signal to the charger/maintainer  24  to resume charging. It should be noted that in certain embodiments, the battery management system  50  may be configured to balance the battery cells  54  any suitable number of times throughout a charging process. Furthermore, the battery management system  50  (and other components of the battery  12 ) may be adapted to implement passive and/or active cell balancing techniques. For example, during passive balancing, the discharged energy from the most charged battery cell or cells may be dissipated as heat. In contrast, during active balancing, energy may be drawn from the most charged battery cell or cells and transferred to the least charged battery cell or cells. For example, the battery management system  50  may include DC-DC converters adapted to transfer the energy from the most charged battery cells to the least charged battery cells. Furthermore, the battery management system  50  may be adapted to implement continuous cell balancing. That is, the battery management system  50  may balance the battery cells  54  during a charging process and while discharging during use. 
     Additionally, the battery management system  50  may be configured to place the battery  12  into a sleep mode to protect the battery cells  54  from damage. For example, the battery management system  50  may electronically control the opening and closing of an internal switch, such as a solid state switch (e.g., a field-effect transistor (FET) or a metal-oxide-semiconductor field-effect transistor (MOSFET)) that may be placed-in line with the terminals  16 . Opening the solid state switch will prevent current flow from the battery  12 , which will disconnect the battery  12  from the vehicle  14  and place the battery  12  into a sleep mode. In particular, the battery management system  50  may be configured to monitor one or more operational parameters of the battery  12  and/or the battery cells  54  and may place the battery  12  into a sleep mode to avoid over-discharge (e.g., under-voltage), over-voltage (e.g., during charging), over-heating, or any other undesirable battery conditions. For example, as will be described in more detail below with respect to  FIG. 7 , the microprocessor  94  may be configured to compare the voltage measured by the voltmeter  90  for each battery cell  54  and/or the voltage measured by the voltmeter  100  to a minimum voltage threshold, and the battery management system  50  may place the battery  12  into a sleep mode in response to a determination that the voltage of the battery  12  is below the minimum voltage threshold to avoid over-discharge of the battery  12 . In certain embodiments, the minimum voltage threshold may be above a minimum voltage for starting the vehicle  14 . Additionally, the microprocessor  94  may be configured to compare the temperature measured by the thermocouple  96  for each battery cell  54  and/or the temperature measured by the thermocouple  104  to a maximum temperature threshold, and the battery management system  50  may force the battery  12  into a sleep mode in response to a determination that the temperature of the battery  12  is greater than the maximum temperature threshold. Furthermore, the battery management system  50  may be configured to place the battery  12  into the sleep mode in response to a signal received from the state of charge indicator  20 . For example, the state of charge indicator  20  may receive a user input (e.g., a user may press a button of the state of charge indicator  20 ) to selectively force the battery  12  into the sleep mode. It may be desirable to enable a user to easily place the battery  12  into the sleep mode if the battery  12  will be unused for a period of time to prevent or minimize discharge of the battery  12 . In the sleep mode, the operation of the battery, charging, discharging, and/or monitoring may change. For example, further discharging may be avoided by electrically uncoupling the input and output conductors of the battery. Similarly, certain monitoring functions may be stopped or placed on a less frequent update basis to conserve energy. In the sleep mode, certain connections to the state of charge indicator (external or installed on the battery) may be maintained, however, to allow for manually re-initiating (“waking”) the battery and/or management system, such as by depressing a momentary contact switch, as discussed below. 
     In addition to monitoring and providing feedback related to the operational parameters, the battery management system  50  may also be configured to store historical data indicative of the operational parameters. In certain embodiments, the battery management system  50  may store a history (e.g., log) of exceptions in the memory  106 . For example, the memory  106  may store information related to events when the voltage, current, and/or temperature of the battery  12  (or one or more of the battery cells  54 ) exceeded a maximum predetermined threshold. In some embodiments, the memory  106  may also store information related to events when the voltage, current, and/or temperature of the battery  12  (or one or more of the battery cells  54 ) was below a minimum predetermined threshold. The memory  106  may store a count of the number of times that the operational parameter (e.g., voltage, current, and/or temperature) was outside of the predetermined thresholds. In certain embodiments, the memory  106  may also store a time stamp and/or duration associated with each event. Furthermore, the memory  106  may be configured to store usage information, such as average load, maximum load on the battery  12 , duration of operation, or other parameters that may be useful for monitoring the operational status of the battery  12 . 
     Exception logging may be desirable to analyze the performance of the battery  12 . For example, the historical data may be useful for post mortem analysis, manufacturing data, sales data, engineering design purposes, or for warranty uses, such as determining whether a replacement battery or refund should be issued. To access the historical data stored in the memory  106 , a data input/output tool  112  may be coupled to the connector  18  and may download data from the memory  106 . The data input/output tool  112  may then analyze the downloaded data or may transmit the data to a processing device, such as a computer, for analysis. Additionally, the data input/output tool  112  may be configured to transmit data to the battery management system  50  for storage in the memory  106 . For example, the data input/output tool  112  may transmit data such as the predetermined thresholds for the operational parameters, algorithms for computing the operational parameters, identification data for the battery  12 , or any other suitable information. 
       FIG. 5  is a partial exploded view of the battery  12  in which the cover  62  is removed from the housing  60  of the battery  12  to illustrate an embodiment of the battery management system  50  and the connector  18 . As illustrated, the connector  18  may be a female pin connector. However, it should be noted that in other embodiments, the connector  18  may be a male connector and/or may be a different type of connector. The connector  18  includes one or more electrical contacts adapted to electrically couple to a complementary connector (e.g., a male pin connector) to transmit signals and/or power across the connector interface. In particular, the connector  18  may be adapted to physically and electrically couple to a connector of the state of charge indicator  20 . Further, the connector  18  may be adapted to physically and electrically couple to a connector of the data input/output tool  112 . To enable the physical and electrical coupling to the state of charge indicator  20  and the data input/output tool  112 , the connector  18  may include a shape (e.g., dimensions and geometry) and pin configuration that is complementary to a shape and pin configuration of the connector of the state of charge indicator  20  and of the connector of the data input/output tool  112 . 
     In certain embodiments, the connector  18  may include a proprietary shape and pin configuration. For example, the connector  18  may be keyed. In one embodiment, the proprietary shape and pin configuration may be selected such that the connector  18  does not couple to any connectors other than the state of charge indicator  20  and the data input/output tool  112 . 
     Furthermore, the connector  18  may include any suitable number of pins (e.g., if the connector  18  is male) or socket contacts (e.g., if the connector  18  is female). In certain embodiments, the connector  18  may include six or seven socket contacts  130 . For example, the connector  18  may include a first socket contact  130  for data input and a second socket contact  130  for data output, which may be adapted to couple to electrical contacts of the data input/output tool  112  or electrical contacts of the state of charge indicator  20 . For example, the first socket contact  130  may be used to download data to the memory  106  of the battery management system  50  from the data input/out tool  112 . Additionally, the second socket contact  130  may be used to transmit historical data relating to exceptions from the memory  106  to the data input/output tool  112 . The connector  18  may also include a third socket contact  130  for power input and a fourth socket contact  130  for power output, which may be adapted to couple to electrical contacts of the state of charge indicator  20 . 
     Further, the connector  18  may include a fifth socket contact  130  and a sixth socket contact  130  to activate one or more indicator lights (e.g., LEDs) of the state of charge indicator  20 . For example, the state of charge indicator  20  may include two indicator lights, such as a red indicator light and a green indicator light. The battery management system  50  may send a signal using the fifth socket contact  130  to activate the green indicator light if the battery management system  50  determines that the state of charge of the battery  12  is above a predetermined threshold. Similarly, the battery management system  50  may send a signal using the sixth socket contact  130  to activate the red indicator light if the battery management system  50  determines that the state of charge of the battery  12  is below a predetermined threshold. The absence of the signals may deactivate the respective indicator light. Additionally, in certain embodiments, the state of charge indicator may include a third indicator light (e.g., a yellow LED), and the battery management system  50  may send a signal over an additional socket contact to activate the yellow indicator light if the battery management system  50  determines that the state of charge of the battery is within a predetermined threshold range. In other embodiments, the battery management system  50  may send a binary signal (e.g., a two-bit or three-bit binary signal) using the fifth socket contact  160  (or any other suitable socket contact) to selectively activate the indicator lights of the state of charge indicator  20  (e.g., a red, green, and/or yellow indicator light). For example, the battery management system  50  may send a first binary signal (e.g., 001) to selectively activate a green indicator of the state of charge indicator  20 , a second binary signal (e.g., 010) to selectively activate a yellow indicator of the state of charge indicator  20 , and a third binary signal (e.g., 100) to selectively activate a red indicator of the state of charge indicator  20 . In such embodiments, the battery management system  50  may send a power signal via the sixth socket contact  130  (or any other suitable socket contact) to power the selectively activated indicator light of the state of charge indicator  20 . 
     Additionally, the connector  18  may include a seventh socket contact  130  adapted to receive a sleep mode signal from the state of charge indicator  20 . However, it should be appreciated that the connector  18  may include additional socket contacts  130  for data input, data output, indicator light control, or any other signals. For example, in other embodiments, an additional socket contact may be used to transmit usage data from the memory  106  to the data input/output tool  112 . 
     Additionally, the connector  18  may conform to a connection standard that provides a high intrusion protection rating. In particular, the shape of the connector  18  and position of the connector  18  may protect the socket contacts from moisture, dirt, and debris. For example, the connector  18  may be recessed in the cover  62  of the battery  12  such that the cover  62  extends past the connector  18  and minimizes exposure to the connector  18 . Further, as illustrated, the connector  18  may be disposed about a side wall  132  of the cover  62 . While the connector  18  may be disposed in other locations of the cover  62 , it may be advantageous to position the connector  18  on a side portion of the cover  62  to further minimize exposure of the connector  18  to moisture, dirt, and debris that may contact the top of the battery cover  62 . 
     The connector  18  is electrically coupled to the battery management system  50  via one or more leads  134 . As illustrated, the battery management system  50  may be disposed between the battery cells  54  and the cover  62  of the battery  12 . The battery management system  50  may be disposed on a support  136 , which may be coupled to the housing  60  and/or the cover  62 . Accordingly, the support  136  may include a plurality of attachment features  138  (e.g., screws) to couple the support  136  to the housing  60  and/or the cover  62 . For example, the support  136  may couple to side walls  140  of the housing  60 . In one embodiment, the support  136  may couple to top portions  142  of the side walls  140 . It should be noted that in some embodiments in which the support  136  couples to the housing  60 , the battery management system  50  is located a distance away from the battery cells  54  such that the battery management system  50  does not contact the battery cells  54 . Disposing the battery management system  50  at a distance away from the battery cells  54  may be advantageous to protect the battery management system  50  from possible electrolyte leakage, overheating, or pressure. Additionally, in some embodiments, the support  136  and the battery management system  50  may be disposed in an interior chamber just under the cover  62  that is formed by the top wall  140  and side walls  132  of the cover  62 . In such embodiments, the support  136  may be secured to the cover  62  or secured to the housing  60  and adapted to extend past the side walls  140  of the housing  60 . In other embodiments, the support  136  may be integral with the housing  60  or the cover  62 . However, the battery management system  50  may be removable from the battery  12 . 
       FIG. 6  is a perspective view of an embodiment of an exemplary state of charge indicator  20  including a connector  160  (e.g., a multi-conductor connector) adapted to couple to the connector  18  of the battery  12 . The connector  160  may be removably coupled (e.g., toollessly removably coupled) to the connector  18  of the battery  12 . As illustrated, the state of charge indicator  20  may be coupled to the connector  160  via the lead  22 . The lead  22  may increase the accessibility of the state of charge indicator  20 . The lead  22  may be any suitable length. For example, the length of the lead  22  may be between approximately one foot and five feet or between approximately two feet and four feet. In one embodiment, the length of the lead  22  may be approximately three feet. 
     As illustrated, the connector  160  may be a male pin connector. However, it should be noted that in other embodiments, the connector  160  may be a female connector and/or may be a different type of connector. The connector  160  may include one or more electrical contacts adapted to electrically couple to the connector  18  to transmit signals and/or power across the connector interface. Accordingly, the connector  160  may include a shape (e.g., dimensions and geometry) and pin configuration that is complementary to the shape and pin configuration of the connector  18  of the battery  12 . In some embodiments, the connector  160  may include a proprietary shape and pin configuration, such as one with a high intrusion protection rating. 
     Additionally, the connector  160  may include any suitable number of pins (e.g., if the connector  160  is male) or socket contacts (e.g., if the connector  160  is female). In certain embodiments, the connector  160  may include six, seven, or eight pins. For example, the connector  160  may include pins for power input, power output, data input, data output, control of indicator lights, and control of a sleep mode switch in the battery  12 . Furthermore, it should be noted that in some embodiments, the connector  18  of the battery  12  may include more electrical contacts than the connector  160 . For example, the connector  18  may include electrical contacts that are adapted to couple to the data input/output tool  112  and are not adapted to couple to the connector  160 . However, the connector  160  may still fit entirely over the connector  18  of the battery  12 . 
     As illustrated, the connector  160  may include a first pin  164  for power input, which may be adapted to transmit power from the battery  12  to the state of charge indicator  20 . In some embodiments, the state of charge indicator  20  may be adapted to operate using power from the battery  12 . For example, the state of charge indicator  20  may include one or more indicator lights, which may use power from the battery  12 . As illustrated, the state of charge indicator  20  includes a first indicator light  166 , a second indicator light  168 , and a third indicator light  170 . The indicator lights may be LEDs, LCDs, organic LEDs, etc. In some embodiments, the first indicator light  166  may a red LED to provide an indication that the state of charge of the battery  12  is low (e.g., less than 10% charged). The state of charge indicator  20  may include a graphic, such as the letter “E”, proximate to the first indicator light  166  to provide a further indication that the first indicator light  166  represents a low state of charge. The second indicator light may be a yellow or orange LED to provide an indication that the state of charge of the battery is deleted (e.g., between 10% and 50% charged). Additionally, the third indicator light  170  may be a green LED to provide an indication that the battery is mostly charged (e.g., at least 50% charged). The state of charge indicator  20  may also include a graphic such as the letter “F”, proximate to the third indicator light  170  to provide a further indication that the third indicator light represents a full state of charge. It should be noted that the state of charge percentages associated with the indicator lights are merely provided as examples and may vary in other embodiments. Further, in some embodiments, the state of charge indicator  20  may feature two indicator lights instead of three. 
     As noted above, the indicator lights may be activated by the battery management system  50  using binary control. In certain embodiments, the battery management system  50  may transmit a signal to the state of charge indicator over a second pin  172  of the connector  160  to selectively activate the first indicator light  166 , the second indicator light  168 , or the third indicator light  170 . By way of example, the battery management system  50  may transmit a first signal (e.g., 001) to selectively activate the first indicator light  166 , a second binary signal (e.g., 010) to selectively activate the second indicator light  168 , and a third binary signal (e.g., 100) to selectively activate the third indicator light  170 . In other embodiments, the battery management system  50  may transmit a power signal over three pins to activate the indicator light associated with the respective pin. For example, as noted above, the battery management system  50  may transmit a power signal over a first pin to activate the first indicator light  166 , a power signal over a second pin to activate the second indicator light  168 , and a power signal over a third pin to activate the third indicator light  170 . As noted above, the absence of the power signals may deactivate the respective indicator light. 
     While the illustrated embodiment relates to indicator lights for providing an indication of the state of charge, it should be noted that in other embodiments, the state of charge indicator  20  may be adapted to provide a numerical indication of the state of charge, a segmented display in which each segment represents a percentage of the state of charge, a single indicator (e.g., an LED or graphic) to provide an indication of a low state of charge, or any other suitable state of charge indication. Further, it should be noted that in other embodiments, the state of charge indicator  20  may also be adapted to provide information relating to other operational parameters of the battery, such as temperature, voltage, and/or current, information relating to the health of the battery, and/or an indication of whether the battery  12  is receiving charge. 
     As noted above, the state of charge indicator  20  interfaces between the battery management system  50  and the charger/maintainer  24 . As such, the state of charge indicator  20  functions as an entry point for the charging system. As illustrated, the state of charge indicator  20  includes a second connector  174  (e.g., a multi-conductor connector) for coupling to the charger/maintainer  24 . The second connector  174  may be directly coupled the body of the state of charge indicator  20 , as illustrated, or may be coupled to the state of charge indicator  20  via a lead. The connector  174  may be any suitable connector, such as a male pin connector, female pin connector, etc. The connector  174  may include a first pin  176  and a second pin  178  adapted to receive power from the charger/maintainer  24 . Additionally, to transmit the power to the battery management system  50 , the connector  160  may include a third pin  180  and a fourth pin  182  for charging the battery  12 . As noted above, the battery management system  50  may be adapted to transmit data (e.g., state of charge data) to the charger/maintainer  24  via the state of charge indicator  20 , which may be used by the charger/maintainer  24  to control the delivery of charge to the battery  12 . Accordingly, the connector  160  may include a fifth pin  184  adapted for data input to receive the data from the battery management system  50 , and the connector  178  may include an additional pin adapted for data output to transmit the received data to the charger/maintainer  24 . However, it should be noted that in some embodiments, the state of charge indicator may not be configured to transmit data from the battery management system  50  to the charger/maintainer  24  and, thus, may not include the fifth pin  184  and the additional pin to facilitate data transfer to the charger/maintainer  24 . 
     Additionally, the connector  160  may include a seventh pin  186  configured to transmit a signal to the battery management system  50  to control a switch (e.g., a solid state switch) to disconnect the battery  12  from the vehicle and force the battery  12  into a sleep mode. In particular, a signal may be transmitted from the state of charge indicator  20  to the battery management system  50  in response to the manual depression of a reset button  190  of the state of charge indicator  20 . Forcing the battery  12  into a sleep mode using the reset button  190  may be advantageous to minimize discharge of the battery  12  during periods of disuse, such as a summer power sports vehicle that is stored over the winter. Additionally, the reset button  190  may function as an antitheft device by disconnecting the battery  12  from the vehicle  14 . In certain embodiments, a signal may be transmitted from the state of charge indicator  20  to the battery management system  50  after the reset button  190  has been depressed for a predetermined amount of time. For example, the state of charge indicator  20  may be adapted to send the signal after the reset button  190  has been depressed for 2 seconds, 3 seconds, 4 seconds, 5 seconds, or any other suitable amount of time. 
     The reset button  190  may also function to reactivate the battery  12 . For example, depression of the reset button  190 , when the battery is in the sleep mode, may cause the state of charge indicator  20  to transmit a signal to the battery management system  50  to control the switch to reconnect the battery  12  to the vehicle  14 . In certain embodiments, the reactivation signal may be transmitted from the state of charge indicator  20  to the battery management system  50  after the reset button  190  has been depressed for a predetermined amount of time. The predetermined amount of time may be the same as or different from the predetermined amount of time to disconnect the battery  12  from the vehicle. For example, the state of charge indicator  20  may be adapted to send the reactivation signal after the reset button  190  has been depressed for 2 seconds, 3 seconds, 4 seconds, 5 seconds, or any other suitable amount of time. 
     While the illustrated embodiment relates to a reset button that may be depressed, in other embodiments, the reset button  190  may be a slide switch or an on/off lever that may be adapted to move between an on state and an off state. In such embodiments, the state of charge indicator  20  may be adapted to transmit a signal to the battery management system  50  immediately following the translation of the switch or lever from an on state to an off state, or vice versa, or may be adapted to transmit the signal after a predetermined amount of time. Further, it should be noted that the reset button  190  may be disposed about any suitable location of the state of charge indicator  20 . 
       FIG. 7  is a flow chart depicting exemplary logic  200  executed by the battery management system  50  for sleep mode control of the battery  12 . As noted above, the battery management system  50  may be configured to monitor the battery  12  to determine whether the battery  12  should be placed into a sleep mode to protect the battery  12 . For example, the battery management system  50  may be adapted to analyze one or more operational parameters of the battery  12  to prevent over-discharge (e.g., under-voltage), over-voltage (e.g., during charging), over-current (e.g., during charging), over-temperature, or any other undesirable battery conditions. Further, the battery management system  50  may be configured to place the battery  12  into a sleep mode in response to a user input. 
     As illustrated, the battery management system  50  may monitor one or more received signals (block  202 ). The one or more received signals may be signals from one or more sensors disposed in the battery  12 . For example, the received signals may be generated by the voltmeter  90  for each battery cell  54 , the thermocouple  96  for each battery cell  54 , the ammeter  98  for each battery cell  54 , the voltmeter  100  of the battery management system  50 , the ammeter  102  of the battery management system  50 , the thermocouple  104  of the battery management system  50 , a voltmeter adapted to measure the input voltage from the charger/maintainer  24 , an ammeter adapted to measure the input current from the charger/maintainer  24 , etc. As described in detail above, the microprocessor  94  may be configured to compute operational parameters of the battery  12  (e.g., voltage, current, temperature, etc.) based on the signals. Additionally, the battery management system  50  may receive one or more signals from the microprocessor  92  of the measurement device  64  for each battery cell  54 , and the signals may include computed operational parameters for the respective battery cell  54 . Further, the battery management system  50  may receive signals from the state of charge indicator  20  in response to the depression of the reset button  190 . 
     As shown in block  204 , the battery management system  50  may be configured to determine whether a user input to place the battery  12  into a sleep mode has been received. For example, if the battery  12  is active and connected to the vehicle  14 , and the battery management system  50  receives a signal from the state of charge connector  20  (e.g., transmitted over the seventh pin  186 ), the battery management system  50  may determine that a user input to place the battery  12  into the sleep mode has been received. Accordingly, in response to the user input, the battery management system  50  may force the battery  12  into sleep mode (block  206 ). In certain embodiments, the battery management system  50  may electronically control the opening and closing of an internal switch, such as a solid state switch (e.g., a field-effect transistor (FET) or a metal-oxide-semiconductor field-effect transistor (MOSFET)), to place the battery  12  into a sleep mode. In such embodiments, opening the switch will prevent current flow from the battery  12 , thereby disconnecting the battery  12  from the vehicle  14  and placing the battery  12  into the sleep mode. 
     If the battery management system  50  does not receive a user input to place the battery into the sleep mode, the battery management system  50  may continue to monitor and analyze the received signals to determine whether the battery  12  should be placed into the sleep mode. For example, the battery management system  50  may determine whether the state of charge of the battery  12  is less than a predetermined threshold (block  208 ). As set forth above, the state of charge of the battery  12  may be determined based on the voltage, current, and/or temperature of the battery  12 . Additionally or alternatively, the battery management system  50  may determine whether the depth of discharge of the battery is greater than a predetermined depth of discharge threshold. Furthermore, in certain embodiments, the voltage of the battery may be used as an approximation of the state of charge of the battery. In certain embodiments, the predetermined threshold may be based at least in part upon the parameters of the battery  12  and the minimum charge for starting the vehicle  14 . For example, if the vehicle  14  requires at least 11 volts to start, the predetermined threshold may be at least 11 volts. In some embodiments, the predetermined threshold may be approximately 11.3 volts. As such, the battery  12  may have an amount of charge sufficient to start the vehicle  14  and to power the vehicle  14  for a period of time until the battery  12  receives charge from the charger/maintainer  24 . If the battery management system  50  determines that the state of charge of the battery  12  is less than the predetermined threshold, the battery management system  50  may force the battery  12  into sleep mode (block  206 ) to prevent over-discharge (e.g., under-voltage). 
     Additionally, the battery management system  50  may be adapted to protect the battery  12  during charging. For example, the battery management system  50  may determine whether an input voltage to the battery  12  from the charger/maintainer is greater than a predetermined threshold (block  210 ). If the battery management system  50  determines that the input voltage to the battery  12  is greater than the predetermined threshold, the battery management system  50  may force the battery  12  into sleep mode (block  206 ) to prevent input over-voltage. Similarly, the battery management system  50  may determine whether an input current to the battery  12  from the charger/maintainer is greater than a predetermined threshold (block  212 ). If the battery management system  50  determines that the input current to the battery  12  is greater than the predetermined threshold, the battery management system  50  may force the battery  12  into sleep mode (block  206 ) to prevent input over-current. It should be noted that the predetermined thresholds for input voltage and input current may be selected based upon the parameters of the battery  12 . 
     Furthermore, the battery management system  50  may be configured to monitor the temperature of the battery  12  to prevent overheating. For example, the battery management system  50  may determine whether the temperature of the battery  12  is greater than a predetermined threshold (block  214 ). As noted above, the temperature of the battery  12  may be determined using the thermocouple  104  and/or the thermocouple  96  of one or more battery cells  54 . If the battery management system  50  determines that the temperature of the battery  12  is greater than the predetermined threshold, the battery management system  50  may force the battery  12  into sleep mode (block  206 ) to prevent overheating. Additionally, the battery management system  50  may determine whether the temperature of the battery  12  and/or the temperature of one or more battery cells  54  of the battery  12  is less than a predetermined threshold (block  216 ). In certain embodiments, it may be desirable for the battery management system  50  to monitor the temperature of the battery  12  and/or the temperature of one or more battery cells  54  during charging, because charging the battery  12  when the temperature is below a predetermined temperature may damage the battery cells  54 . For example, charging certain lithium batteries when the temperature of the battery is below zero degrees Fahrenheit may damage the battery cells. Thus, the battery management system  50  may force the battery into sleep mode (block  206 ) to prevent damage to the battery cells (e.g., during charging) if the battery management system  50  determines that the temperature is below the predetermined threshold. 
     Moreover, it should be noted that in certain embodiments, the battery management system  50  may be configured to consider a combination of operating parameters to determine whether to transition the battery  12  to the sleep mode (block  206 ). In certain embodiments, the battery management system  50  may transition the battery  12  to the sleep mode if two or more operating parameters (e.g., temperature, state of charge, depth of discharge, input voltage, input current, etc.) violate a respective predetermined threshold. By way of example, if the battery temperature is 110 degrees Fahrenheit and all other operating parameters do not violate a respective predetermined threshold, the battery management system  50  to may not transition the battery  12  to sleep mode. Additionally, if the voltage is 14.8 volts and all other operating parameters do not violate a respective predetermined threshold, the battery management system  50  to may not transition the battery  12  to sleep mode. However, if the battery temperature is 110 degrees Fahrenheit and the voltage is 14.8 volts, the battery management system  50  may transition the battery to the sleep mode. 
     As noted above, the reset button  190  of the state of charge indicator  20  may also be used to reactivate the battery  12 .  FIG. 8  is a flow chart depicting exemplary logic  230  executed by the battery management system  50  for reactivation of the battery  12 . As illustrated, the battery management system  50  may receive a signal from the state of charge indicator  20  to reactivate the battery  12  (block  232 ). As noted above, depressing the reset button  190  of the state of charge indicator  20  may generate a signal that causes the battery management system  50  to alter the state of the internal switch (e.g., from open to closed or vice versa). Thus, if the battery  12  is in the sleep mode, the received signal may cause the battery management system  50  to close the switch and reactivate the battery  12  (block  234 ). 
     In some embodiments, a condition may have been detected, such as under-voltage, input over-voltage, input over-current, or over-heating, that caused the battery management system  50  to place the battery  12  into sleep mode. This condition may still be present when the battery  12  is reactivated. Accordingly, the battery management system  50  may implement the sleep mode control logic  200  to continue to monitor the operational parameters of the battery  12  and protect the battery  12  from undesirable operating conditions after the battery  12  is reactivated. As such, if the condition (e.g., under-voltage, input over-voltage, input over-current, or over-temperature) persists after the battery  12  is placed into sleep mode and then reactivated, the battery management system  50  may place the battery  12  back into the sleep mode to avoid damage to the battery  12 . 
     While only certain features and embodiments of the disclosure have been illustrated and described, many modifications and changes may occur to those skilled in the art (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosed embodiments. Furthermore, in an effort to provide a concise description of the embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the disclosed embodiments, or those unrelated to enabling the claimed disclosed embodiments). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.