Abstract: The invention relates to a traction battery having a first battery cell group and a second battery cell group. A first connection of the first battery cell group is connected to a first battery pole by a charging and disconnecting device, a second connection of the first battery cell group is connected to a first service plug connection, a first connection of the second battery cell group is connected to a second service plug connection, and a second connection of the second battery cell group is connected to a second battery pole by a disconnecting device. The first service plug connection and the second service plug connection can be short-circuited by an external service plug.

Abstract: A cell management system and method for balancing energy across a plurality of cells coupled to a circuit bus. The system can include a transformer, two transformer switches, and for each cell, a first switch pair allowing transfer of energy between the transformer and the cell, and a second switch pair allowing removal or inclusion of the cell in the serial connection of cells. The system can include an energy storage device, a switch pair allowing transfer of energy between the transformer and the storage device, and for each cell, a third switch pair allowing transfer of energy between the storage device and the cell. The system can include cell, bus and storage device sensors and state estimators. The system can include a controller that controls the transformer switches, cell switches, and storage device switches based on the sensor readings and states.

Abstract: An apparatus for powering an electric hand-held power tool device by an output voltage includes at least two connectors for connecting the apparatus to at least two batteries. At least two switches, and a command circuit of the switches, are provided. The command circuit is arranged for commanding the powering of the electric hand-held power tool device by using the battery which presents the highest open circuit voltage if the output voltage is higher than the open circuit voltage of each of the other batteries. And, by using the battery which presents the highest open circuit voltage and at least one other battery if the output voltage is lower than the open circuit voltage of the other battery, the battery which presents the highest open circuit voltage and the at least one other battery being connected in parallel.

Abstract: A method of balancing current in a vehicle electric system having a system bus, a first battery, a first bi-directional battery voltage converter selectively transferring a first current between the first battery and the system bus, a second battery, a second bi-directional battery voltage converter selectively transferring a second current between the second battery and the system bus, and a controller controlling the first bi-directional battery voltage converter and the second bi-directional battery voltage converter. The method includes sensing the first current and sensing the second current. The first bi-directional battery voltage converter and the second bi-directional battery voltage converter are controlled so that the first current and the second current are equal portions of a load current supplied to an electrical load connected to the system bus.

Abstract: A personal solar appliance (PSA) is presented that collects and stores solar energy. A method of charging a battery from a solar cell according to some embodiments is presented that includes applying power from a bootstrap circuit when the battery has a very low state of charge or the solar cell has output below a threshold; and applying power from a maximum power point circuit when the battery and the solar cell provide power above the threshold.

Abstract: A battery system includes: a battery unit formed by electrically connected in series a plurality of cell groups each made up with a plurality of battery cells electrically connected in series; a plurality of sensing lines for detecting voltages of respective battery cells in the battery unit; an integrated circuit provided to each of the cell group, to which the sensing lines for detecting voltages of respective battery cells in the cell group are connected; a case having housed therein a substrate at which a plurality of integrated circuits provided for the cell groups respectively are mounted; noise protection capacitors disposed between input terminals of the plurality of sensing lines; and at least one protection element against static electricity which is connected between the input terminals and the case.

Abstract: An electricity storing device includes a high-voltage terminal, a low-voltage terminal, a plurality of rechargeable battery modules, a plurality of first switches each coupled between one rechargeable battery module and the high-voltage terminal, a plurality of second switches each coupled between one rechargeable battery module and the low-voltage terminal, a plurality of third switches each coupled between two of the rechargeable battery modules, and a control module for outputting a control command to control couplings of the plurality of first switches, the plurality of second switches and the plurality of third switches.

Abstract: A charge-balancing system includes N circuits and a control module, where N is an integer greater than or equal to 1. Each of the N circuits includes first and second switches connected in series and an inductance having a first end connected between the first and second switches. The control module outputs control signals to control the first and second switches. A second end of the inductance of a first one of the N circuits is connected between two cells of a first pair of 2N series-connected cells of a battery stack. The first and second switches of the first one of the N circuits are connected in parallel to the first pair of 2N series-connected cells.

Abstract: A protection device includes a voltage detector having N or more sub-circuits each for monitoring a specific battery cell to output a detection signal when at least one of the battery cells outputs an abnormal voltage. Each sub-circuit includes voltage dividing resistors, a reference voltage generator, and a comparator. The voltage dividing resistors generate a voltage division signal by dividing an output voltage of the battery cell. The reference voltage generator generates a reference voltage. The comparator compares the voltage division signal against the reference voltage. Each comparator is powered with voltage across the battery cell associated with the sub-circuit.

Abstract: A charge balancing circuit implemented within a charge storage device (cell) in a series connected charge storage unit (battery) made up of a plurality of cells. The charge balancing circuit may utilize a controller to sense the voltage in the cell it is implemented therein and the cells adjacent thereto. If the voltage of the current cell exceeds a threshold voltage and is greater than at least one adjacent cell the current cell can transfer charge to the adjacent cell having the lowest voltage. The transfer of the charge is done with a switching network that extracts current from the current cell and then transfers the current to the adjacent cell having the lowest voltage. The switching network may utilize switches and a current storage device (inductor) to transfer the charge. The controller may activate different switches based on which adjacent cell has the lowest voltage.

Abstract: A battery control circuit includes an electronic switch, first and second diodes, and first and second batteries. A positive terminal of the first battery is connected to a positive terminal of the second battery through the first diode. A negative terminal of the first battery is connected to a positive terminal of the second battery through the electronic switch, and connected to a negative terminal of the second battery through the second diode. When the electronic switch receives a first control signal, the electronic switch is turned on, the first and second diodes are turned off, and the first and second batteries are connected in series. When the electronic switch receives a second control signal, the electronic switch is turned off, the first and second diodes are turned on, and the first and second batteries are connected in parallel.

Abstract: A dynamically reconfigurable battery framework for management of a large-scale battery system systems is provided. The framework monitors, reconfigures, and controls large-scale battery systems online. The framework is built upon a topology-based bypassing mechanism that provides a set of rules for changing the battery-pack configuration, and a semantic bypassing mechanism by which the battery-cell connectivity is reconfigured to recover from a battery-cell failure. More specifically, the semantic bypassing mechanism implements a constant-voltage-keeping policy and a dynamic-voltage-allowing policy. The former policy is effective in preventing unavoidable voltage drops during the battery lifetime, while the latter policy is effective in supplying different amounts of power to meet a wide-range of application requirements.

Abstract: A system and method for equalizing a battery pack during a battery pack charging process in accordance with an exemplary embodiment is provided. The method includes receiving total capacity estimates for all battery cells in the battery pack, and receiving state-of-charge estimates for all battery cells in the battery pack. The method further includes computing an equalization metric for all battery cells in the battery pack. The method further includes determining an equalization action for all battery cells in the battery pack, and initiating that equalization action. The method further includes executing a battery pack charging step.

Abstract: A four-stage power distribution system (100) includes (i) a first stage (110) having an inverter (112) that provides power to a frequency drive (114) and an electric motor (116) controlled by the frequency drive; (ii) a second stage (120) having a flywheel (122) driven by the motor; (iii) a third stage (130) having an alternator (132) driven by the motor (116) and connected to the flywheel, and a rectifier (134) that receives current from the alternator and generates a direct current; and (iv) a fourth stage (140) having a charge control switch (142) that receives power from the rectifier, and a plurality of power storage devices such as batteries (144A-144C). A master control switch (150) controls the charge control switch to transition the plurality of batteries individually between a charging configuration and a load configuration. One or more of the battery(ies) in the load configuration provides power to the inverter.

Abstract: Systems and methods are herein disclosed for efficiently and cost-effectively balancing the voltages across batteries and/or cells in an energy storage system. A controller monitors the battery voltages and instructs regulator circuits to balance voltages between any batteries or sets of batteries having imbalanced voltages. Regulator circuits implementing a modified ?uk converter can be utilized. Regulator circuits can have two capacitive circuits, one inductive circuit, and two switches. Two capacitors, an inductor, and two field effect transistors can be used in each regulator circuit.

Abstract: A voltage detecting circuit includes a switch group that selects any one of a plurality of battery cells connected in series, a sampling capacitor that maintains a potential difference between a positive electrode terminal and a negative electrode terminal of a battery cell selected by the switch group, a measuring part that outputs a detected voltage value signal corresponding to the potential difference between ends of the sampling capacitor, a transfer switch that transfers, to the measuring part, the potential difference caused between the ends of the sampling capacitor, a correction capacitor provided in parallel to input terminals of the measuring part, and between the transfer switch and the measuring part, and a discharge switch provided in parallel to the correction capacitor, and controlled so that a switching condition of the discharge switch is mutually exclusive with that of the transfer switch.

Abstract: Disclosed is a circuit arrangement. The circuit arrangement includes a plurality of rechargeable batteries each having at least one rechargeable electrochemical cell, and current-carrying members connecting the plurality of batteries such that when the plurality of batteries are charging the plurality of batteries are in a series electrical circuit arrangement and when the plurality of batteries are discharging the plurality of batteries are in a parallel electrical circuit arrangement.

Abstract: A battery pack having multiple cells connected through “virtual” connections via MOSFETs, other insulated-gate field-effect transistors, and the like. The use of virtual connections allows for the use of one or more “spare” battery cells, which may be swapped in for underperforming cells or to take discharged cells offline for charging. A microprocessor monitors and manages individual battery cells or batteries in an array. The battery pack of the present disclosure may further include an optional cooling system and/or a novel encapsulation to protect the cells and electronics from use in harsh environments.

Abstract: In an electric power supply system, a plurality of batteries (405, 406) are connected in series by a switch group (402 to 404, 407 to 409), and a higher voltage and a lower voltage are output through a terminal and a VOL terminal, respectively, and are respectively converted in the voltage thereof by two step-down DC-DC inverters (105, 106). During a discharge operation upon a serial connection, remaining content of the batteries is measured in a period other than the period of discharge from the batteries (105, 106), and the connection mode of the serial connection is controlled based on the remaining content, to control the discharge of the respective batteries up to the discharge capacity.

Abstract: The invention provides an energy storage system having storage elements linked for collective charging and discharging. Monitoring circuitry is provided for monitoring each of the storage elements independently. Preferably, the system includes control circuitry configured for controlling the linking of individual storage elements in order to enhance system performance. In preferred embodiments, the system also includes storage elements in an arrangement whereby they may be selectably linked and delinked, in series, parallel, or in one or more series/parallel combination.

Abstract: A balancing method for a battery pack includes balancing battery cells near an end of discharge. A deep discharge of the battery cells can be prevented without using an overdischarge control unit. One battery cell balancing method includes: a balancing check condition determination step for determining whether or not a maximum voltage out of voltages of the battery cells is smaller than a reference voltage; a balancing start condition determination step for determining whether or not a residual capacity difference or voltage difference between the individual battery cells exceeds a reference value; a balancing time calculation step for calculating a balancing time for discharging the battery cell that exceeds the reference value; and a balancing operation step for discharging the selected battery cell when the battery cells are under charge or are at rest or when a discharge current of the battery cells is smaller than a reference current.

Abstract: A dynamically reconfigurable framework is provided for a large-scale battery system. The framework is comprised of a plurality of battery circuits arranged adjacent to each other to form a battery-cell array that is coupled to an application load. A given battery circuit includes: a battery cell with an input terminal and an output terminal; a first switch connected between the load and an input terminal of the battery cell; a second switch is connected between an input terminal of the battery cell and an output terminal of a battery cell in an immediately adjacent battery circuit; and a third switch connected between the output terminal of the battery cell and the output terminal of the battery cell in the adjacent battery circuit. The battery-cell array also includes a local controller that selectively controls the switches in the plurality of battery circuits.

Abstract: A dynamically reconfigurable battery framework for management of a large-scale battery system systems is provided. The framework monitors, reconfigures, and controls large-scale battery systems online. The framework is built upon a topology-based bypassing mechanism that provides a set of rules for changing the battery-pack configuration, and a semantic bypassing mechanism by which the battery-cell connectivity is reconfigured to recover from a battery-cell failure. More specifically, the semantic bypassing mechanism implements a constant-voltage-keeping policy and a dynamic-voltage-allowing policy. The former policy is effective in preventing unavoidable voltage drops during the battery lifetime, while the latter policy is effective in supplying different amounts of power to meet a wide-range of application requirements.

Abstract: A power source with multiple cells connected in parallel to a common node or power supply point. The individual cells within the power source may also have a dedicated controller for each of the individual cells. Additionally, a system controller is coupled to each controller in a feedback loop and is configured to selectively connect each cell of the plurality of cells to a power bus to control the discharge of each of the plurality of cells.

Abstract: There is provided a battery system having a plurality of storage batteries capable of charging and discharging, and at least two or more of the storage batteries are connected in series. The battery system includes a connecting terminal capable of connecting a storage battery in parallel with any one of the other storage batteries. The battery system is capable of replacing the storage battery without restricting the configuration to be serial connection or parallel connection, while avoiding decline of the output power.

Abstract: A battery pack is provided. In one embodiment, the battery pack includes a plurality of battery units each including at least one battery cell, a charge switch unit for connecting the plurality of battery units in parallel to form a charge path, a discharge switch unit for connecting the plurality of battery units in series to form a discharge path, and a battery management unit for controlling switching of the charge switch unit and the discharge switch unit according to a standby mode, a charge mode, a and discharge mode of the battery pack. The switching is controlled with a delay time associated with each of combinations of mode conversion between the modes.

Abstract: A portable terminal is provided having an external module that is capable of easily charging a battery of the external module, such as a bluetooth, and of easily checking the charged status thereof. The charged status of a second battery of the external module may be displayed through a terminal body as well as the charged status of a first battery, thereby being capable of easily recognizing when the external module is required to be charged.

Abstract: According to one embodiment, a secondary battery device includes a first assembled battery including a plurality of secondary battery cells, a second assembled battery including a plurality of secondary battery cells and connected in series to a low-potential terminal of the first assembled battery, a disconnecting module capable of mechanically switching connection between the first assembled battery and the second assembled battery, a voltage measurement circuit configured to measure voltages of the plurality of secondary battery cells of the second assembled battery, a first power source wiring connected between a high-potential terminal of the second assembled battery and the voltage measurement circuit, a second power source wiring connected between a low-potential terminal of the second assembled battery and the voltage measurement circuit, and a filter connected between the first power source wiring and the second power source wiring.

Abstract: A protection circuit device for a battery having secondary batteries connected in series. A reference voltage circuit generates a reference voltage and a voltage detection circuit for detecting a voltage of one of the secondary batteries and comparing the detected voltage with the reference voltage generated by the reference voltage circuit to thereby detect an over-charge state and an over-discharge state of the one of the secondary batteries. Each of the reference voltage circuit and the voltage detection circuit has a power supply terminal connected to a positive electrode of the one of the secondary batteries and has a ground terminal connected to a negative electrode of the one of the secondary batteries. A withstand voltage of elements forming the reference voltage circuit and the voltage detection circuit is set to be lower than an overall voltage of the secondary batteries.

Abstract: A cell balancing circuit for balancing battery cells includes a transformer and a switching controller. The transformer has a primary winding and a secondary winding. The switching controller can select a first cell coupled to the primary winding and select a second cell coupled to the secondary winding. The first cell and the second cell are coupled in series. The first cell has a cell voltage that is greater than the second cell. The cell balancing circuit further includes a controller coupled to the primary winding. The controller controls energy from the first cell to the primary winding so as to transfer the energy from the first cell to the second cell to balance the battery cells.

Abstract: A cell management system and method for balancing energy across a plurality of cells coupled to a circuit bus. The system can include a transformer, two transformer switches, and for each cell, a first switch pair allowing transfer of energy between the transformer and the cell, and a second switch pair allowing removal or inclusion of the cell in the serial connection of cells. The system can include an energy storage device, a switch pair allowing transfer of energy between the transformer and the storage device, and for each cell, a third switch pair allowing transfer of energy between the storage device and the cell. The system can include cell, bus and storage device sensors and state estimators. The system can include a controller that controls the transformer switches, cell switches, and storage device switches based on the sensor readings and states.

Abstract: The present invention provides a battery array voltage equalization device comprising: a sampling unit which samples the battery voltage signals of the battery array according to a sampling control signal; an analog-to-digital converting unit which converts the sampled voltage signals into a digital voltage signal; a control unit which generates the sampling control signal and a driving signal based on the digital voltage signal; an equalization unit which equalizes the voltage signals of the battery array based on the driving signal; a filter unit which is connected to the equalization unit and the battery array. The present invention applies the filter unit to filter out the ripple signal generated during equalization.

Abstract: A battery assembly having batteries connected in series to form rows and columns of battery cells into packs that combine the energy of multiple batteries. The battery cells are joined together to form columns of cells connected mechanically together by an exterior connection sleeve, and mechanically and electrically connected together by a conductive epoxy joining the end of one cell to the end of an adjacent cell in series. The columns of cells are mounted and held in place by racks, with bolts passing through the racks to form a sandwich structure that secures the position and orientation of the cells and columns, and that maintains the electrical connection between joined cells. Perpendicularly disposed to the direction of the columns are a series of conductive bands that join adjacent cells together along rows of cells.

Abstract: A reconfigurable battery has at least one bank of statically joined series connected battery cells, each cell including a positive and a negative pole. The poles connect through switches to respective output connections. Activating a set of processor controlled switches reconfigures at least some of the battery cells into a configuration to provide a voltage across the output connections. The output battery voltage may vary intermediately between open circuit voltage and the maximum voltage produced by the series connected battery cells. An alternative configuration of switches divides groups of series connected battery cells into separate battery banks that permit other battery cell configurations. Duty cycle modulation of the switches allows intermediate control of output voltage with reduced switching transients. Reconfigurable battery cells used in combination with an electric motor permit selectable speed control and battery regeneration schemes matched to motor output.

Abstract: A voltage balancer device has a plurality of discharge paths. Each pair of the discharge paths correspond to each secondary battery unit. Each of a pair of the discharge paths has a resistance of a different value. Discharging the voltage of each secondary battery unit is at first performed through the discharge path of a smaller resistance value. The voltage balancer device switches the currently used discharge path to another discharge path having a large resistance value at the time the voltage of the secondary battery unit nearly equal a desired voltage.

Abstract: A system for energizing an energy storage device includes an electric power source, an energy system in communication with the electric power source, and a switching time control multiplexer. The energy storage system includes at least two parallel energy storage devices. The switching time control multiplexer is configured to supply total charging current from the electric power source to the energy storage system such that each storage device is charged in an alternating manner with the total charging current being less than a total charging current required for parallel charging.

Abstract: The invention relates to a storage battery (4) comprising at least first and second branches (Br1, Br2) each having at least first (E1,1, E1,2) and second (E2,1, E2,2) storage cells connected in series, the battery further comprising a switch (D2,1) by means of which the first storage cells are connected in parallel and by means of which the second storage cells are connected in parallel, the cut-off threshold of the switch being designed to conduct the current when one of said storage cells forms an open circuit.

Abstract: A contact array arrangement which both receives charging current for charging batteries of a battery pack, and which also breaks the parallel charging contact position (contact configuration in which individual batteries of the battery pack are charged in parallel) then reestablishes series connection of the batteries when a charge electrode array is urged against the contact array arrangement and when the charge electrode array is removed. A cover covering the contact array may be connected by throughbolts to a support supporting series connection contacts such that depressing the cover by imposing a downward force (e.g., the weight of a charge electrode array), moves the series connection contacts out of contact with those contacts receiving charge current. Springs return the series connection contacts to the series condition. Charge conductors fixed to the contact array pass through or by the series connection such that a very compact device results.

Abstract: An automotive power supply system comprises a battery module that includes serially connected battery groups each constituted with serially connected battery cells, integrated circuits each disposed in correspondence to one of the battery groups, a control circuit, a transmission path through which the integrated circuits are connected to the control circuit and a relay circuit via which an electrical current is supplied from the battery module. In response to a start signal instructing an operation start and received via the transmission path, each integrated circuit measures terminal voltages at the individual battery cells in the corresponding battery group and executes an abnormality diagnosis. If abnormality diagnosis results provided by the integrated circuits indicate no abnormality, the control circuit closes the relay, enabling supply of electrical current from the battery module and subsequently, the control circuit receives measurement results from the integrated circuits via the transmission path.

Abstract: A fuel cell system that includes a fuel cell stack and an EESD electrically coupled to a common high voltage bus line. The EESD has a higher voltage output than the fuel cell stack, and thus the stack is unable to fully charge the EESD, for example, at system shut-down. In order to allow the fuel cell stack to fully charge the EESD, the EESD is separated into a plurality of separate electrical storage banks having lower voltage potentials. A series of contactors are provided to electrically couple the storage banks in series during normal system operation, and separately charge the storage banks using the fuel cell stack so that they are fully charged. The series of contactors can also be configured so that the storage banks can be electrically coupled in series during normal operation of the system and be electrically coupled in parallel during charging at system shut-down.

Abstract: A motor vehicle includes an on-board vehicle electric system, an electric consumer, whose resistance decreases with the decreasing voltage dropping at the consumer, an electric energy accumulator, and a switching arrangement. The switching arrangement is designed and is connected or connectable to the on-board vehicle electric system, the consumer and the energy accumulator such that in a first switching position, the energy accumulator, and in a second switching position, the switching arrangement, is connected in parallel to the on-board vehicle electric system. The energy accumulator in the second switching position is connected in series to the consumer, and the energy accumulator in the first switching position is not connected in series to the consumer.

Abstract: A power source with multiple cells connected in parallel to a common node or power supply point. The individual cells within the power source may also have a dedicated controller for each of the individual cells such that the dedicated controllers are connected on a one to one basis with each of the respective individual cells.

Abstract: A body-insertable apparatus includes: an illuminating unit that illuminates the inside of a subject's body; an imaging unit that takes an image of the inside of the subject's body; a first power supplying unit that supplies electric power to the imaging unit; a second power supplying unit that supplies electric power to the illuminating unit; and a switch that either connects the first power supplying unit to the second power supplying unit or disconnects the first power supplying unit from the second power supplying unit. The switch electrically separates the first power supplying unit from the second power supplying unit during at least an illuminating period of the illuminating unit.

Abstract: This disclosure includes battery systems and operational methods. According to one aspect, a battery system includes conversion circuitry, a plurality of main terminals configured to be coupled with a load, a charger and a plurality of rechargeable battery modules which are coupled in series with one another intermediate the main terminals, switching circuitry configured to couple a first of the battery modules with an input of the conversion circuitry, and the conversion circuitry being configured to modify an electrical characteristic of electrical energy received from the first of the battery modules and to output the electrical energy having the modified characteristic to a second of the battery modules.

Abstract: A voltage sensing device with which high-precision voltage sensing is possible without the need to obtain a unique correction constant for each device. A pair of voltage input nodes NCk and NCk-1 is selected from voltage input nodes NC0-NCn in switch part 10, and they are connected to sensing input nodes NA and NB in two types of patterns with different polarity (forward connection, reverse connection). Sensing input nodes NA and NB are held at reference potential Vm by voltage sensing part 20, and current Ina and Inb corresponding to the voltage at voltage input nodes NCk and NCk-1 flows to input resistors RIk and RIk-1. Currents Ina and Inb are synthesized at different ratios in voltage sensing part 20, and sensed voltage signal S20 is generated according to the synthesized current Ic. Sensed voltage data S40 with low error is generated according to the difference between the two sensed voltage signals S20 generated in the two connection patterns.

Abstract: A charge control apparatus for controlling how to charge a battery unit having a plurality of batteries connected in series, includes a connection control section that divides the batteries into a plurality of groups of batteries by switching connections between the batteries, according to a received current amount indicative of an amount of a current that can be received from one or more external power sources, and a charge control section that charges the groups of batteries in parallel with power received from the external power sources.

Abstract: A fast charge configuration for a power supply includes a serial connection to a pair of batteries each having an output that is half that required by the device, such as the electric vehicle, in which the batteries are to be used.

Abstract: A system may include a switchover element configurable to source or sink power from or to an electronic device electrically coupled to the switchover element and a controller in communication with the switchover element. The controller may be configured to determine if the electronic device is healthy. When the electronic device is healthy, the controller may configure the switchover element to deliver power from the electronic device to the system and configure the switchover element to provide the power to any unhealthy electronic device electrically coupled to the system.

Abstract: A method for extending the service life of a portable device includes monitoring a battery of a portable device; identifying a problem bank; reconfiguring a connection schema for the battery to replace the problem battery bank with at least one spare bank; conditioning or exercising the problem bank; connecting the portable device to a power supply to recharge the problem bank; and reconnecting the recharged or repaired bank according to the connection schema without the at least one spare bank. A method for extending the service life of a portable device includes monitoring power consumption of at least one of the hardware or software of a portable device; and reconfiguring the connection schema of the battery banks to redistribute power consumption of at least one of the hardware or software.

Abstract: This invention provides an electrical charge and discharge circuit suitable for supplying power for backup operation function to a system power source with use of a battery module for low voltage. The battery modules are connected in parallel, in case of charging to the battery modules, and the battery modules are serially connected, in case of discharging charged power and supplying power to the load. This invention also comprises a contact switch provided between a plus terminal and a minus terminal of the battery module connected serially at discharge.