Abstract:
Disclosed herein are battery systems for electric vehicles. An electric vehicle may include a first battery. The first battery may be configured to power various low voltage systems. For example, the first battery may provide the power to start the vehicle. The vehicle may include a second battery. The second battery may be configured to power one or more electric motors for propelling the vehicle. The first battery may supply power necessary to engage and/or access the power stored in the second battery. The first battery may include a heater to ensure that the first battery can supply ample power to initiate a start sequence in low temperatures.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is related to Attorney Docket No. FARA.020A, entitled “FLEXIBLE CIRCUIT FOR VEHICLE BATTERY,” Attorney Docket No. FARA.022A, entitled “BUS BAR AND PCB FOR VEHICLE BATTERY,” and Attorney Docket No. FARA.023A, entitled “ELECTRIC VEHICLE BATTERY,” filed on the same day as the present application. Each of the above-referenced applications is hereby expressly incorporated by reference in its entirety and for all purposes. 
       BACKGROUND 
       [0002]    Field 
         [0003]    This disclosure relates to vehicle battery systems, and more specifically to systems and methods for providing heat to battery cells for improved cold-weather operation. 
         [0004]    Description of the Related Art 
         [0005]    Electric vehicles, hybrid vehicles, and internal combustion engine vehicles generally contain a low voltage automotive battery to provide power for starting the vehicle and/or to provide power for various other electrically powered systems. Automotive batteries typically provide approximately 12 volts, and may range up to 16 volts. Such batteries are typically lead-acid batteries. In electric or hybrid vehicles, a low voltage automotive battery may be used in addition to higher voltage powertrain batteries. 
       SUMMARY 
       [0006]    The systems and methods of this disclosure each have several innovative aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope as expressed by the claims that follow, its more prominent features will now be discussed briefly. 
         [0007]    An electric vehicle may include a first battery. The first battery may be configured to power various low voltage systems. For example, the first battery may provide the power to start the vehicle. The vehicle may include a second battery. The second battery may be configured to power one or more electric motors for propelling the vehicle. The first battery may supply power necessary to engage and/or access the power stored in the second battery. The first battery may include a heater to ensure that the first battery can supply ample power to initiate a start sequence in low temperatures. 
         [0008]    In some implementations, a low voltage battery for an electric vehicle includes a battery housing enclosing a plurality of electrochemical cells disposed therein. A heat source may be disposed within the battery housing. The heat source may be configured to increase the temperature of the plurality of electrochemical cells when activated. A temperature sensor may be disposed within the housing. The sensor may be configured to measure the temperature of at least one of the plurality of electrochemical cells. Circuitry may also be disposed within the housing. The circuitry may be in communication with the temperature sensor and/or the heat source. The circuitry may be configured to receive temperature information from the temperature sensor and control the heat source based at least in part on the received temperature information. 
         [0009]    In some aspects, the plurality of electrochemical cells have a minimum operating temperature. The circuitry may be configured to activate the heat source when the temperature sensor measures a temperature lower than the minimum operating temperature. The circuitry may be configured to deactivate the heat source when the temperature sensor measures a preselected deactivation temperature that is greater than or equal to the minimum operating temperature. The circuitry may be configured to deactivate the heat source after a preselected maximum heating time. 
         [0010]    In some implementations, an electric vehicle may include a battery heating system disposed within the vehicle. A first battery may include a housing, a plurality of electrochemical cells within the housing, and a heat source within the housing. A second battery may also be disposed within the battery. The second battery may be located in a different position than the first battery. For example, the first battery may be positioned in the front half of the vehicle while the second battery may be positioned in the rear half of the vehicle. The first battery may have a first voltage battery that is configured to provide power to engage the second battery. The second battery may be configured to provide power to the heat source. 
         [0011]    Some implementations include a method of starting an electric vehicle. The method may include one or more of the following steps. For example, the method may include transmitting power from a first battery of an electric vehicle to engage a second battery of the electric vehicle. The method may include transmitting power from the second battery to a heat source disposed within the first battery. The method may include warming the first battery with the heat source. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The above-mentioned aspects, as well as other features, aspects, and advantages of the present technology will now be described in connection with various implementations, with reference to the accompanying drawings. The illustrated implementations are merely examples and are not intended to be limiting. Throughout the drawings, similar symbols typically identify similar components, unless context dictates otherwise. 
           [0013]      FIG. 1  is a top perspective view of an assembled low voltage automotive battery in accordance with an exemplary embodiment. 
           [0014]      FIG. 2  is a cross sectional view of an assembled battery of  FIG. 1 . 
           [0015]      FIG. 3  is an exploded view of an automobile battery of  FIG. 1 . 
           [0016]      FIG. 4  is a perspective view of the lower portion of the battery of  FIG. 1  as prepared for final assembly in accordance with an exemplary embodiment. 
           [0017]      FIG. 5  is a perspective view of the upper portion of the battery of  FIG. 1  prepared for final assembly in accordance with an exemplary embodiment. When assembled, the top portion may be inverted from its position shown in  FIG. 5  and placed on top of the lower portion shown in  FIG. 4  to form an assembled housing as shown in  FIG. 3 . 
           [0018]      FIG. 6  is a partial cutaway perspective view of the battery of  FIG. 1  illustrating the primary electrical connections of the battery in accordance with an exemplary embodiment. 
           [0019]      FIG. 7  is a perspective view of a lower housing body and baseplate of the battery of  FIG. 1  including a heat source in accordance with an exemplary embodiment. 
           [0020]      FIG. 8A  is a perspective view of the housing baseplate of the battery of  FIG. 1  including a heat source in accordance with an exemplary embodiment. 
           [0021]      FIG. 8B  is a perspective view of the housing baseplate of the battery of  FIG. 1  including a configuration of a heat source and a plurality of electrochemical cells in accordance with an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    The following description is directed to certain implementations for the purpose of describing the innovative aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein can be applied in a multitude of different ways. In some implementations, the word “battery” or “batteries” will be used to describe certain elements of the embodiments described herein. It is noted that “battery” does not necessarily refer to only a single battery cell. Rather, any element described as a “battery” or illustrated in the Figures as a single battery in a circuit may equally be made up of any larger number of individual battery cells and/or other elements without departing from the spirit or scope of the disclosed systems and methods. 
         [0023]    Reference may be made throughout the specification to “12 volt” power systems or sources. It will be readily apparent to a person having ordinary skill in the art that the phrase “12 volt” in the context of automotive electrical systems is an approximate value referring to nominal 12 volt power systems. The actual voltage of a “12 volt” system in a vehicle may fluctuate as low as roughly 4-5 volts and as high as 16-17 volts depending on engine conditions and power usage by various vehicle systems. Such a power system may also be referred to as a “low voltage” system. Some vehicles may use two or more 12 volt batteries to provide higher voltages. Thus, it will be clear that the systems and methods described herein may be utilized with battery arrangements in at least the range of 4-34 volts without departing from the spirit or scope of the systems and methods disclosed herein. 
         [0024]    To assist in the description of various components of the battery systems, the following coordinate terms are used (see, e.g.,  FIGS. 2-5 ). A “longitudinal axis” is generally parallel to the longest dimension of the battery housing embodiments depicted. A “lateral axis” is normal to the longitudinal axis. A “transverse axis” extends normal to both the longitudinal and lateral axes. For example, the cross sectional view of  FIG. 2  depicts a plurality of cylindrical cells; each cell is oriented parallel to the transverse axis, while the cells are oriented in a row of seven cells along a line parallel to the longitudinal axis. 
         [0025]    In addition, as used herein, “the longitudinal direction” refers to a direction substantially parallel to the longitudinal axis, “the lateral direction” refers to a direction substantially parallel to the lateral axis, and the “transverse direction” refers to a direction substantially parallel to the transverse axis. 
         [0026]    The terms “upper,” “lower,” “top,” “bottom,” “underside,” “top side,” “above,” “below,” and the like, which also are used to describe the present battery systems, are used in reference to the illustrated orientation of the embodiment. For example, as shown in  FIG. 2 , the term “top side” may be used to describe the surface of the battery housing containing the positive and negative terminal posts, while the term “bottom” may be used to describe the location of the baseplate. 
         [0027]    Traditional gasoline powered cars typically include a low voltage SLI (starting, lighting, ignition) battery. Similarly, electric vehicles may include a low voltage SLI battery along with a high voltage battery system having significant energy storage capacity and suitable for powering electric traction motors. The low voltage battery may be necessary to provide the startup power, power an ignition, close a high voltage battery contactor, and/or power other low voltage systems (e.g. lighting systems, electronic windows and/or doors, trunk release systems, car alarm systems, and the like). 
         [0028]    In addition to powering the vehicle&#39;s propulsion motors, the high voltage batteries&#39; output may be stepped down using one or more DC-to-DC converters to power some or all of the other vehicle systems, such as interior and exterior lights, power assisted braking, power steering, infotainment, automobile diagnostic systems, power windows, door handles, and various other electronic functions when the high voltage batteries are engaged. 
         [0029]    High voltage batteries may be connected to or isolated from other vehicle circuitry by one or more magnetic contactors. Normally open contactors require a power supply in order to enter or remain in the closed circuit position. Such contactors may be configured to be in the open (disconnected) configuration when powered off to allow the high voltage batteries to remain disconnected while the vehicle is powered off. Thus, on startup, a small power input is required to close at least one contactor of the high voltage battery pack. Once a contactor is closed, the high voltage batteries may supply the power required to keep the contactor(s) closed and/or supply power to other vehicle systems. 
         [0030]    Particular embodiments of the subject matter described by this disclosure can be implemented to realize one or more the following potential advantages. Rather than using a traditional lead-acid automobile battery, the present allows for a smart rechargeable battery that does not require a fluid filled container. In some aspects, one or more individual cells in a housing may be monitored individually or in subsets. In some aspects, additional individual cells may be provided within the housing such that the connected cells can provide more voltage than necessary to compensate for the potential of the loss of one or more of the cells. The disclosed design may be easier and/or less expensive to manufacture. For example, the number of manufacturing steps may be minimized and the labor may be simplified and/or made more efficient. For example, two halves of a battery housing may be assembled separately and electrical components may later be coupled together in one final step when the two housing halves are combined. Such a construction may minimize the number of sealing steps while sensitive parts are contained within the housing. A desiccant may be provided to remove excess moisture in the housing in order to further protect the electric components and/or cells within the housing. A valve may help prevent unsafe pressures from building up within the housing. In some aspects, the housing may be designed such that the parts inside the housing are inhibited from moving excessively and/or vibrating excessively while a vehicle is operated. 
         [0031]    These, as well as, other various aspects, components, steps, features, objects benefits, and advantages will now be described with reference to specific forms or embodiments selected for the purposes of illustration. It will be appreciated that the spirit and scope of the cassettes disclosed herein is not limited to the selected forms. Moreover, it is to be noted that the figures provided herein are not drawn to any particular proportion or scale, and that many variations can be made to the illustrated embodiments. 
         [0032]      FIG. 1  is a top perspective view of an assembled battery  100  in accordance with an exemplary embodiment. The exterior of the lid  102  of the battery housing  101  includes a positive terminal post  104 , a negative terminal post  106 , a terminal post protection structure  108 , a CAN connector  110 , and a pressure vent  112 . The positive terminal post  104  and negative terminal post  106  are connected to the interior components via internal bus bars and circuitry as described with reference to  FIGS. 1 and 2 . 
         [0033]    The terminal post protection structure  108  may be formed as a single piece with the housing lid, for example, by molding or 3D printing. The protection structure  108  is provided in order to protect the terminal posts  104  and  106  from unintentional or harmful contact. In addition, the protection structure  108  can prevent inadvertent creation of a short circuit between the terminal posts  104  and  106 . For example, if a vehicle owner or mechanic drops a metal tool across the terminal posts  104  and  106  while performing maintenance, a short circuit is created. If the owner or mechanic attempts to retrieve the tool while it is in contact with both posts  104  and  106 , severe electric shock may result. Thus, the terminal post protection structure  108  should include a longitudinal portion raised in the transverse direction far enough that a straight metal tool cannot touch both terminal posts  104  and  106  at the same time. 
         [0034]    The valve  112  may be a waterproof pressure relief valve, such as a GORE protective vent. A waterproof pressure relief valve may allow the pressure within the battery housing to equalize with the outside air pressure while preventing the low-humidity atmosphere within the battery  100  from being compromised. The valve  310  is described in greater detail with reference to  FIG. 2 . 
         [0035]      FIG. 2  depicts a cross sectional view of an assembled battery  100  in accordance with an exemplary embodiment. The unitary battery housing  101  comprises a lid  102  and a lower portion including an upper housing body  114 , a lower housing body  116 , and a baseplate  118 . The lid  102  includes the pressure vent  112 , negative terminal post  106 , terminal post protection structure  108 , and an opening  109  for the CAN connector  110 , as shown in the exterior view of  FIG. 1 . 
         [0036]    Within the housing  101 , the CAN connector  110  may be in electrical communication with a monitoring and control PCB  120 . The terminal post  106  is in electrical contact with a bus bar  122 . Other circuitry (not shown) in electrical contact with the bus bar  122  is further connected electrically to a plurality of electrochemical cells  124 . A desiccant holder  126  may also be located within the housing  101 . 
         [0037]    The cross sectional view of  FIG. 2  illustrates several advantages of the battery  100  over conventional designs. The unitary housing  101  provides a sealed environment for all internal components of the battery  100 . In many existing automotive battery designs, the battery components are held in place by an internal structure, with an additional external protective structure, or blast shield, required to protect the battery  100  and maintain the desired interior conditions. Instead, the present battery housing  101  may contain integrated interior structural components to eliminate the need for additional interior components. For example, the lower housing body  116  described above may include an integrated lower cell holder framework  128 , comprising an array of cylindrical openings sized to secure one end of each of the electrochemical cells  124 . Similarly, the upper housing body  114  described above may include an integrated upper cell holder framework  130 , comprising an array of cylindrical openings sized and arranged identically to the openings of the lower cell holder framework  128 , so as to secure the opposite end of each of the electrochemical cells  124 . Thus, the cells  124  may be held in place within the housing  101 . In some embodiments, the portion of the lower space surrounding the cells  124  may be filled with an electronics potting compound to further secure the cells  124  in place and/or to reduce the effects of vibrations or other mechanical stresses on the battery  100 . The potting compound may be any suitable gelatinous or solid compound, such as a silicone or other rubber gel, thermal setting plastics, epoxy, or the like. 
         [0038]    The battery housing  101  will preferably be sealed or substantially sealed at all joints and ports so as to provide a stable environment for the electrochemical cells  124 . Pressure and humidity variations may have significant detrimental effects on the battery  100 . More specifically, the interior of the battery  100  should be kept at substantially the same pressure as the ambient air pressure to avoid excessive wear to the battery housing, seals, or other components. The interior of the housing  101  should also be kept relatively dry, as condensation or excess humidity may shorten battery life. Thus, a combination of environmental features may be provided to optimize moisture and pressure conditions within the battery  100 . 
         [0039]    Environmental control features may include a waterproof pressure relief valve  112 , such as a GORE protective vent, a desiccant contained within the desiccant holder  126 , and/or a heat source  144 . The heat source  144  may be located in a lower portion of the battery  100  and provide heat to the electrochemical cells  124  to aid in cold temperature operation of the battery  100 . The configuration and operation of the heat source is explained in greater detail with reference to  FIGS. 7, 8A, and 8B . The waterproof pressure relief valve  112  may allow the pressure within the battery housing  101  to equalize with the outside air pressure while preventing liquids from entering the battery  100 . Although some moisture may enter the battery  100  as air passes through the waterproof valve  112 , the moisture may be removed within the battery  100  by a desiccant in the desiccant holder  126 . 
         [0040]    The desiccant within the battery housing  101  can be configured to absorb any moisture initially inside the housing  101  after manufacture, and may later absorb moisture from the air entering the battery housing  101  through the waterproof pressure valve  126  or a crack or hole in the material of the housing  101 . In some embodiments, the upper cell holder framework  130  may also serve as a support for the desiccant holder  126 . The desiccant holder  126  may be located near the cells  124  within the battery housing  101  so as to most effectively dry the air around the cells  124 . However, the desiccant holder may be effective if located in any location within the battery housing  101 . 
         [0041]    The desiccant within the desiccant holder  126  may include a variety of desiccating or hygroscopic materials, such as silica gel, calcium sulfate, calcium chloride, activated charcoal, zeolites, Drierite, or any other suitable desiccant. 
         [0042]      FIG. 3  depicts an exploded view of the automotive battery  100  expanded along the transverse axis. As shown, the battery  100  includes a plurality of electrochemical cells  124  contained within a housing comprising a housing lid  102 , an upper housing body  114 , a lower housing body  116 , and a housing baseplate  118 , which can be joined, sealed, or welded to form a unitary battery housing. The upper housing body  114  has an upper edge  115 . The lid  102  has an upper surface  103  and a lower edge  105 . During manufacturing, the upper edge  115  of the upper housing body may be sealingly fitted into, around, or against the lower edge  105  of the lid  102 . Such a seal may be formed, for example, using an appropriate sealant, adhesive, weld, vibratory weld, and the like. The lid  102  includes terminal post protection structure  108  on its upper surface  103 . 
         [0043]    The housing may further contain a desiccant holder  126 . A desiccant holder cover  127  may help contain the desiccant within the desiccant holder  126 . Such a cap  127  may removably coupled to the desiccant holder  126  via a snap-fit, screw-fit, or other similar configuration. The housing may also contain a heat source  144 , which may be coupled to the housing baseplate  118  adjacent to the electrochemical cells  124 . 
         [0044]    Continuing with  FIG. 3 , a positive bus bar  121  and a negative bus bar  122  are disposed within the upper housing body  114  and/or the lid  102 , and in electrical contact with the electrochemical cells  124  via connecting pins  132  and other circuitry (not shown). Terminal posts  104  and  106  extend through the housing lid  102  to the exterior of the battery  100  and are in electrical communication with the positive bus bar  121  and the negative bus bar  122 . The terminal posts  104  and  106  are secured by terminal post fasteners  134 . The bus bars  121  and  122  may be held to the lid  102  by flanges  123  and  125  and secured with fasteners  136  and inserts  138 . Monitoring and control printed circuit board (PCB)  120  is disposed within an upper portion of the housing and may be configured to monitor the actual voltage across each cell  124  or a set of cells  124 , or to monitor the current flowing into or out of the battery  100  through bus bars  121  and  122 . The PCB may include elements such as a terminal power header  140  and a thermistor connector  142 . The PCB  120  is in electrical communication with the CAN connector  110  which extends through the housing lid  102  at opening  109  to the exterior of the battery  100 . The PCB  120  may be supported in place by the CAN connector  110  as well as by the lid  102  and/or bus bars  121  and  122 , and may be secured to the lid  102  and/or bus bars  121  and  122  by fasteners  136 . 
         [0045]    The electrochemical cells  124  are configured to provide direct current power. In some embodiments, the cells  124  may provide sufficient voltage to power a nominal 12-volt automotive power system. The cells  124  may be any variety of electrochemical cell, such as lithium ion, nickel metal hydride, lead acid, or the like. In some embodiments with multiple electrochemical cells  124 , the cells  124  may be arranged in any combination of parallel and series connections. For example, a battery delivering a maximum of 15.6 volts may include a single string of four 3.9-volt cells connected in series, multiple 4-cell serial strings connected in parallel, or four serially connected strings of multiple parallel cells, so as to provide a greater energy storage capacity at the same voltage of 15.6 volts. 
         [0046]    The housing components  102 ,  114 ,  116 , and  118  may be assembled at various times during manufacturing to form one housing structure. In some embodiments, housing components  102 ,  114 ,  116 , and  118  may be glued or otherwise adhered together to form a single housing unit. In embodiments where the housing components are made of a plastic, the housing components may be joined by any suitable variety of plastic welding, such as hot gas welding, hot plate welding, contact welding, speed tip welding, laser welding, solvent welding, or the like, to form a robust protective housing. In some embodiments, the housing may be an integrated unit containing internal structure such as compartments for the electrochemical cells  124 , so as to avoid the additional weight and complexity associated with having separate internal structural components. 
         [0047]    With reference to  FIGS. 4 and 5 , a simplified battery assembly process will now be described. In some aspects, the simplicity and efficiency of the battery assembly process are a result of various battery features described elsewhere herein.  FIG. 4  depicts a lower portion  150  of a battery before final assembly.  FIG. 5  depicts a lid  102  of a battery before final assembly, in an inverted orientation. A lower portion housing  151  may include the housing components  114 ,  116 , and  118  described above, and may be manufactured with an upper interior framework  130  and lower interior framework  128  (not shown) for holding a plurality of electrochemical cells  124  and a desiccant holder  126 , as described above with reference to  FIGS. 2 and 3 . 
         [0048]    The lid  102  may be prepared for assembly by securing a negative bus bar  122  and a positive bus bar  121  (not shown) within the lid  102  with positive and negative terminal posts  104  (not shown) and  106  (not shown) connected to the bus bars  121  (not shown) and  122 , and extending through the housing lid  102 . Each bus bar has a connecting pin  132  configured to connect with circuitry of the lower portion  150  of the battery during assembly. A PCB  120  for battery monitoring and control may then be secured to the housing lid  102  and/or bus bars  121  (not shown) and  122  with a CAN connector  110  connecting to the PCB  120  through the housing lid  102 . 
         [0049]    With a completed battery lid  102  and lower battery portion  150 , final assembly of the battery is straightforward and suitable for completion on an assembly line or similar high-capacity production line. The plurality of electrochemical cells  124  are inserted into the cylindrical openings in the interior framework  130  of the lower portion housing  151 , and a desiccant holder  124  containing desiccant is inserted into the appropriate opening. Circuitry (not shown) configured to connect the cells  124  to the bus bars  121  and  122  may be placed on top of the cells  124 . In a final assembly step, the lid  102  is turned upright, placed atop the lower portion  150  and pressed downward to couple the lower edge  105  of the housing lid to the upper edge  115  of the lower portion housing  151 . At the same time, bus bar connecting pins  132  will form a press-fit connection to circuitry (not shown) of the lower portion  150 , completing the electrical connection between the terminal posts and the electrochemical cells  124  via the bus bars  121  and  122 , connecting pins  132 , and other circuitry. The housing lid  102  and lower portion housing  151  are sealed at their intersection by any suitable form of plastic welding to complete the assembly. 
         [0050]      FIG. 6  depicts a cutaway view of a battery  100  showing only the primary electrical connections of the battery  100  after final assembly. As used herein, the term “primary electrical connections” of the battery  100  refers to the conductive path between the electrochemical cells  124  and the terminal posts  104  and  106 , by which the electrochemical cells  124  provide nominal  12  volt electrical power to various vehicle systems. Thus, the primary electrical connections do not include other conductive connections to the battery circuit such as control or monitoring systems. The primary electrical connections include the electrochemical cells  124 , connecting pins  132 , bus bars  121  and  122 , terminal posts  104  and  106 , and other circuitry (not shown) connecting the cells  124  to the connecting pins  132 . For clarity, the baseplate  118  and lower housing body  116  are also depicted. Thus, current can flow between the negative terminal post  106  and the negative terminal of the cells  124  by traveling through the negative bus bar  122 , connecting pin  132 , and other circuitry (not shown). Similarly, current can flow between the positive terminal of the cells  124  and the positive terminal post  104  by traveling through the other circuitry (not shown), connecting pin  132 , and positive bus bar  121 . 
         [0051]      FIG. 7  is a perspective view of a lower housing body  116  and baseplate  118  of the battery of  FIG. 1  including a heat source  144  in accordance with an exemplary embodiment. As described above, the lower housing body  116  may include an integrated lower cell holder framework  128  configured to secure the lower end of a plurality of electrochemical cells (not shown). In some embodiments, the heat source  144  may be a substantially flat heating pad which may be secured between the baseplate  118  and the cell holder framework  128  of the lower housing body  116 . The heating pad may be a resistive heating pad. Thus, the heat source  144  may be secured in a desired location adjacent to the end surface of the electrochemical cells (not shown) without requiring additional fasteners, adhesives, or other securing means to avoid unintended movement of the heat source  144 . 
         [0052]      FIG. 8A  is a perspective view of a battery housing baseplate  118  with a heat source  144  in accordance with an exemplary embodiment.  FIG. 8B  depicts an arrangement of the baseplate  118  and heat source  144  of  FIG. 8A  with the addition of a plurality of electrochemical cells  124  in an exemplary operative configuration. The heat source  144  may provide heat to the electrochemical cells  124 . 
         [0053]    Cold temperatures may reduce the performance and/or charging ability of various types of battery cells  124 . For example, lithium ion cells charge and operate poorly at low temperatures sometimes experienced by automobiles during the winter. More specifically, temperatures below approximately −20° C. may decrease or inhibit discharging. Temperatures below 0° C. may prohibit charging entirely. Thus, a heat source  144  may be necessary for the use of lithium-ion cells in a 12-volt automotive power system. 
         [0054]    When battery power or charging is desired, but the cells  124  are colder than a desired minimum operating temperature, such as 0° C. in some embodiments, the heat source  144  may activate to warm the cells  124  to an acceptable operating temperature. A low temperature condition may be detected with a temperature sensor (not shown) and battery monitoring circuitry (not shown). Battery monitoring circuitry (not shown) may be located near or within the heat source  144 , or may be located elsewhere, such as in the battery monitoring printed circuit board described above. The temperature sensor (not shown) may be located within or adjacent to at least one of the electrochemical cells  124  in order to accurately measure the temperature of the cells. One or more temperature sensors may be used. For example, the temperature sensors may include one or more thermistors, thermocouples, or other temperature sensing devices. In various embodiments, temperature sensors may be placed directly adjacent to an exterior surface of one or more cells  124 , and may be secured against the surface with an adhesive tape or other suitable securing means. 
         [0055]    After a period of heating, the temperature sensor (not shown) and battery monitoring circuitry (not shown) may detect that the cells have reached an acceptable operating temperature. In some implementations, the battery monitoring circuitry may comprise the PCB  120  (shown, for example in  FIG. 3 ). In response, the battery monitoring circuitry (not shown) may deactivate the heat source  144 , and the cells  124  may begin or continue to charge and/or provide power. Continued operation of the cells  124  may generate enough heat to maintain an acceptable operating temperature without further use of the heat source  144 . If continued operation does not generate enough heat due to very low ambient temperature or insufficient current draw, the heat source  144  may be reactivated to maintain an acceptable operating temperature. 
         [0056]    In some embodiments, the heat source  144  may operate with a predetermined maximum heating time to avoid runaway or excessive heating conditions. For example, a failure of the temperature sensor (not shown) may cause a false low temperature indication even after the cells  124  have reached an acceptable operating temperature. A false low temperature indication may result in the circuitry (not shown) causing the heat source  144  to continue heating the cells  124  until damage or failure occurs. However, a predetermined maximum heating time will ensure that the heat source  144  stops heating the cells  124  before damage can occur. 
         [0057]    The heat source  144  may be disposed adjacent to the battery housing baseplate  118 . In some embodiments, the baseplate  118  may comprise transverse extensions  146  configured to extend through the heat source  144  to prevent longitudinal or lateral motion of the heat source  144 . Preferably, the heat source  144  will be in thermal contact with a surface of the cells  124 . In some embodiments, the heat source  144  may be in thermal contact with the lower end surfaces of the cells  124 , or may be in thermal contact with the side surfaces of the cells  124 . The arrangement of a heat source  144  in thermal contact with the cells  124  increases the efficiency of heating the cells  124  by allowing the cells  124  to be rapidly warmed to an acceptable operating temperature without having to warm the entire space within the battery housing  101 . 
         [0058]    The heat source  144  may provide heat to the electrochemical cells  124  by direct contact, thermal radiation, or similar heat transfer processes. The heat source  144  may be a single heating element  144  contacting the bottom of all cells  124 , or may include multiple smaller heating elements  148 . For example, in some embodiments including a plurality of cylindrical electrochemical cells  124 , the heat source may include a plurality of circular heating elements  148 , each sized and shaped to heat the circular end surface of a single cell  124 . The plurality of circular heating elements  148  may be arranged in an array within a generally flat heating pad  144  such that each heating element  148  is located where it will contact the lower surface of a cell  124 , either directly or with one or more layers of heat conducting material between the cell  124  and the heating element  148 . It is noted that where a heat source  144  is placed against one circular end surface of a cylindrical cell  124 , it may be necessary for both the positive and negative terminals of the cell  124  to be located together on the opposite circular end surface of the cell  124 . 
         [0059]    The heat source  144  may require electrical power to provide heat to the cells  124 . Electrical power for the heat source  144  may be provided by the cells  124 . For example, when the temperature is too cold for charging or optimal discharging, the cells  124  may still be able to provide enough current to activate the heat source  144  long enough to warm the cells  124  to a preferred temperature. In electric vehicles, the heat source  144  may be configured to draw electrical power from high voltage batteries of the electric vehicle. For example, the cells  124  at a low temperature may still be able to provide enough current to activate the high voltage powertrain batteries. The activated high voltage batteries can then provide power to the heat source  144 , either directly or through a DC-to-DC converter. 
         [0060]    The foregoing description details certain embodiments of the systems, devices, and methods disclosed herein. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the devices and methods can be practiced in many ways. As is also stated above, it should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to including any specific characteristics of the features or aspects of the technology with which that terminology is associated. The scope of the disclosure should therefore be construed in accordance with the appended claims and any equivalents thereof. 
         [0061]    With respect to the use of any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 
         [0062]    It is noted that the examples may be described as a process. Although the operations may be described as a sequential process, many of the operations can be performed in parallel, or concurrently, and the process can be repeated. In addition, the order of the operations may be rearranged. A process is terminated when its operations are completed. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. 
         [0063]    The previous description of the disclosed implementations is provided to enable any person skilled in the art to make or use the present disclosed process and system. Various modifications to these implementations will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of the disclosed process and system. Thus, the present disclosed process and system is not intended to be limited to the implementations shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.