JP5507946B2 - Battery control unit - Google Patents

Description

  The present invention relates to a battery control unit that controls a battery that supplies power to a load.

  Conventionally, there is a power distribution system that supplies electric power from a battery to various loads. The battery in the power distribution system is used not only for the storage of surplus power but also as emergency power during a commercial power outage. For example, in the power distribution system disclosed in Patent Document 1, the following battery charge / discharge control is performed in preparation for an emergency such as a power failure. That is, a predetermined state of charge (SOC) is secured in advance as emergency power in the battery. The SOC is an index indicating the remaining battery rate, and is represented by a numerical value of 0 to 100%. When the SOC is 100%, the battery is fully charged, and when the SOC is 0%, the remaining capacity of the battery is zero. Accordingly, when the SOC of the battery becomes a predetermined value, for example, 20% or less due to the discharge, the subsequent discharge is stopped and the charging is started. With this control, emergency power can be reliably ensured, and power can be supplied to the minimum necessary load even during a power failure.

JP 2009-159730 A

  By the way, the said battery deteriorates by repeating charging / discharging. As the battery deteriorates, the effective capacity of the battery decreases. For example, it is assumed that the effective capacity of a new battery is 100 Wh, but the effective capacity of the battery is reduced by 20 Wh due to deterioration, and the effective capacity is 80 Wh. In such a situation, even if only 20% of the SOC of the battery is secured in preparation for an emergency, the remaining capacity of the battery varies depending on the presence or absence of deterioration. Specifically, a new battery secures an electric energy of 20 Wh, whereas the deteriorated battery secures only an electric energy of 16 Wh. This problem becomes more prominent as the battery deteriorates. As described above, since the amount of power secured in an emergency is reduced due to the deterioration of the battery, there is a possibility that the amount of power required in an emergency cannot be secured.

  The present invention has been made in view of such circumstances, and an object of the present invention is to reliably secure the amount of battery power required for emergency use.

Hereinafter, means for achieving the above-described object and its operation and effects will be described.
The invention according to claim 1 controls a plurality of batteries for supplying electric power to an electric load, and discharge and charging of the plurality of batteries, and the battery group for normal use in which the plurality of batteries are normally used. And an effective capacity detecting means for detecting an effective capacity of the emergency battery group, in a battery control unit comprising: a control unit assigned as the emergency battery group used at the time of a power failure, and the effective capacity The detecting means calculates a discharge amount at a timing when a predetermined battery remaining rate is reached with respect to a fully charged state for the emergency battery group, and the emergency battery group is based on the battery remaining rate and the discharged amount. detecting the effective capacity of use of the battery groups, the control unit, based on said detection result of the effective capacitance detection unit, missing effective capacity of the battery group of the emergency is And when it is determined, and the gist thereof to increase the number of the battery to be allocated for very automatically.

  According to the configuration, when it is determined that the effective capacity of the emergency battery group is insufficient due to battery deterioration or the like, at least one of the normal battery groups is added to the emergency battery group. It is done. As a result, the effective capacity of the emergency battery group can be increased, and a sufficient amount of power can be secured in preparation for a power failure.

  According to a second aspect of the present invention, in the battery control unit according to the first aspect, the effective capacity detection means is a current voltage detection means for detecting a discharge current and a battery voltage of the emergency battery group, and When the emergency battery group is discharged at a predetermined timing, the control unit calculates a discharge amount based on the detection result of the current / voltage detection means, and the calculated discharge amount is required at the time of power failure. When it becomes less than the discharge threshold set based on the discharge amount when discharged at the effective capacity of the battery group, it is determined that the effective capacity of the emergency battery group is insufficient, and The main point is to increase the number of batteries allocated for emergency use.

  According to this configuration, the discharge amount is calculated based on the discharge current and battery voltage of the emergency battery group detected by the current / voltage detection means. Here, as the effective battery capacity of the battery decreases due to deterioration, the discharge amount of the battery decreases. Therefore, it is possible to determine whether the effective capacity of the battery group is sufficient based on the comparison between the discharge amount of the emergency battery group and the discharge threshold. Here, the discharge threshold is set based on the amount of discharge when discharged with the effective capacity required at the time of a power failure. That is, when the discharge amount of the emergency battery group is less than the discharge threshold, it is determined that the effective capacity of the battery group is insufficient, and the number of emergency batteries is automatically increased. Thereby, the effective capacity | capacitance of the battery group for emergency can be increased, and sufficient electric energy can be ensured at the time of a power failure.

  According to the present invention, in the battery control unit, it is possible to ensure the amount of battery power required for emergency use.

The block diagram which shows the structure of the power distribution system in this embodiment. The block diagram which expanded a part of FIG. 1 in this embodiment. The graph which showed the relationship between the voltage Vb and SOC in this embodiment. The flowchart which shows the process sequence of the emergency power ensuring program in this embodiment.

Hereinafter, a first embodiment in which a battery control unit according to the present invention is embodied in a power distribution system will be described with reference to FIGS.
As shown in FIG. 1, a home is provided with a power distribution system 1 that supplies power to various devices (such as lighting devices, air conditioners, home appliances, and audiovisual devices) installed in the home. The power distribution system 1 supplies various devices with electric power of a solar cell 3 that generates power using sunlight in addition to electric power of a commercial AC power supply (AC power supply) 2 for home use. Further, the power distribution system 1 also uses a fuel cell 4 that generates power by a chemical reaction of substances as a power source. The power distribution system 1 supplies power not only to the DC device 5 that operates by inputting a DC power supply (DC power supply) but also to the AC device 6 that operates by inputting an AC power supply (AC power supply).

  The power distribution system 1 is provided with a control unit 7 and a DC power distribution board (built-in DC breaker) 8 as a power distribution board of the system 1. The power distribution system 1 is provided with a control unit 9 and a relay unit 10 as devices for controlling the operation of the DC device 5 in the house.

  An AC distribution board 11 for branching an AC power supply is connected to the control unit 7 via an AC power line 12. The control unit 7 is connected to the commercial AC power supply 2 and the fuel cell 4 through the AC distribution board 11 and is connected to the solar cell 3 through the DC system power line 13. The control unit 7 takes in AC power from the AC distribution board 11 and DC power from the solar cell 3 and converts these powers into predetermined DC power as a device power source. Then, the control unit 7 outputs the converted DC power to the DC distribution board 8 via the DC system power line 14 or outputs it to the battery unit 16 via the DC system power line 15 and supplies the same power. To store electricity. The battery unit 16 is used as a backup power source at the time of a power failure, for example. The control unit 7 not only takes in AC power but also converts DC power of the solar cell 3 and the battery unit 16 into AC power and supplies it to the AC distribution board 11. The control unit 7 exchanges data with the DC distribution board 8 via the signal line 17.

  The DC distribution board 8 is a kind of breaker that supports DC power. The DC distribution board 8 branches the DC power input from the control unit 7 and outputs the branched DC power to the control unit 9 via the DC power line 18 or relays via the DC power line 19. Or output to the unit 10. Further, the DC distribution board 8 exchanges data with the control unit 9 via the signal line 20 and exchanges data with the relay unit 10 via the signal line 21.

  A plurality of DC devices 5 are connected to the control unit 9. These DC devices 5 are connected to the control unit 9 via a DC supply line 22 that can carry both DC power and data by a pair of lines. The DC supply line 22 superimposes a communication signal for transmitting data by a high-frequency carrier wave on a DC voltage serving as a power source for the DC device, so-called power line carrier communication. Transport to. The control unit 9 acquires the DC power supply of the DC device 5 via the DC power line 18 and controls which DC device 5 based on the operation command obtained from the DC distribution board 8 via the signal line 20. Know what to do. Then, the control unit 9 controls the operation of the DC device 5 by outputting a DC voltage and an operation command to the instructed DC device 5 via the DC supply line 22.

  A switch 23 that is operated when switching the operation of the DC device 5 in the house is connected to the control unit 9 via a DC supply line 22. In addition, a sensor 24 that detects a radio wave transmitted from an infrared remote controller, for example, is connected to the control unit 9 via a DC supply line 22. Therefore, not only the operation instruction from the DC distribution board 8 but also the operation of the switch 23 and the detection of the sensor 24, a communication signal is sent to the DC supply line 22 to control the DC device 5.

  A plurality of DC devices 5 are connected to the relay unit 10 via individual DC power lines 25, respectively. The relay unit 10 acquires the DC power supply of the DC device 5 through the DC power line 19 and determines which DC device 5 is to be operated based on an operation command obtained from the DC distribution board 8 through the signal line 21. To grasp. The relay unit 10 controls the operation of the DC device 5 by turning on / off the power supply to the DC power line 25 with respect to the instructed DC device 5 using a built-in relay. In addition, a plurality of switches 26 for manually operating the DC device 5 are connected to the relay unit 10, and the DC power line 25 is turned on and off by the relay by operating the switch 26, thereby enabling the DC unit 5 to operate the DC unit 5. The device 5 is controlled.

  The DC distribution board 8 is connected to a DC outlet 27 built in a house in the form of a wall outlet or a floor outlet, for example, via a DC power line 28. If a plug (not shown) of a DC device is inserted into the DC outlet 27, DC power can be directly supplied to the device.

  Further, between the AC distribution board 11 and the commercial AC power supply 2, a power meter 29 capable of remotely metering the usage amount of the commercial AC power supply 2 is connected. The power meter 29 is equipped with not only a function of remote meter reading of the amount of commercial power used, but also a function of power line carrier communication and wireless communication, for example. The power meter 29 transmits the meter reading result to an electric power company or the like via power line carrier communication or wireless communication.

  The power distribution system 1 is provided with a network system 30 that enables various devices in the home to be controlled by network communication. The network system 30 is provided with a home server 31 as a control unit of the system 30. The home server 31 is connected to a management server 32 outside the home via a network N such as the Internet, and is connected to a home device 34 via a signal line 33. The in-home server 31 operates using DC power acquired from the DC distribution board 8 via the DC power line 35 as a power source.

  A control box 36 that manages operation control of various devices in the home by network communication is connected to the home server 31 via a signal line 37. The control box 36 is connected to the control unit 7 and the DC distribution board 8 via the signal line 17 and can directly control the DC device 5 via the DC supply line 38. For example, a gas / water meter 39 capable of remotely metering the amount of gas used or the amount of water used is connected to the control box 36 and also connected to the operation panel 40 of the network system 30. The operation panel 40 is connected to a monitoring device 41 including, for example, a door phone slave, a sensor, and a camera.

  When the in-home server 31 inputs an operation command for various devices in the home via the network N, the home server 31 notifies the control box 36 of the instruction, and operates the control box 36 so that the various devices operate in accordance with the operation command. . The in-home server 31 can provide various information acquired from the gas / water meter 39 to the management server 32 through the network N, and accepts from the operation panel 40 that the monitoring device 41 has detected an abnormality. This is also provided to the management server 32 through the network N.

  Next, a specific configuration around the control unit 7 and the battery unit 16 will be described. As shown in FIG. 2, the control unit 7 includes a solar cell DC-DC converter (hereinafter referred to as a solar cell converter) 53 and a bidirectional converter 58.

The solar cell converter 53 converts the DC power input from the solar cell 3 into appropriate DC power and outputs the DC power to the DC distribution board 8 and the bidirectional converter 58.
The bidirectional converter 58 converts the DC power from the solar cell 3 and the battery unit 16 into AC, and also converts the AC power from the AC power source 2 and the fuel cell 4 into DC.

The battery unit 16 includes a control unit 51, a first DC-DC converter (hereinafter referred to as a first converter) 55, a second DC-DC converter (hereinafter referred to as a second converter) 56,
The first to eighth batteries 61 to 68, a switching device 59, a current detection sensor 70, and a voltage detection sensor 71 are included.

  In this example, the effective capacities of the batteries 61 to 68 when they are new are equal, and the batteries 61 to 68 are formed of battery cells. In the initial setting, the first to fourth batteries 61 to 64 are assigned for emergency use at the time of a power failure, and the fifth to eighth batteries 65 to 68 are assigned for normal use at a normal time. .

  The control unit 51 includes a non-volatile memory 51a, and an emergency power securing program, various threshold values, and the like described later are stored in the memory 51a. Further, the control unit 51 includes a timer 51b that measures the discharge time T. The control unit 51 outputs a command signal related to discharging to the first converter 55 and outputs a command signal related to charging to the second converter 56. Based on the command signal, the first converter 55 converts the power from the first to eighth batteries 61 to 68 into appropriate power for the DC power line 14 and outputs the power, and the second converter 56 outputs the command signal. Based on this, the electric power from the DC power line 14 is converted into appropriate electric power for the first to eighth batteries 61 to 68 and output.

  In addition, switching device 59 is provided between first to eighth batteries 61 to 68 and both converters 55 and 56, and based on a command signal from control unit 51, first to eighth batteries 61 to 68 are connected to both converters. The switching operation connected to 55 and 56 is performed. That is, the switching device 59 includes a plurality of switching elements. In the initial setting, the control unit 51 connects the normal fifth to eighth batteries 65 to 68 to the converters 55 and 56 in series, and the emergency first to fourth batteries 61 to 64 are connected to the converters. 55 and 56 are not connected. Although the first to fourth batteries 61 to 64 are fully charged in preparation for an emergency, the power from the first to fourth batteries 61 to 64 is not connected to both the converters 55 and 56. It is not supplied to the DC device 5 or the like.

The current detection sensor 70 is provided on the DC power line 15, detects the output current I 1 of the first converter 55, and outputs the detection result to the control unit 51.
The voltage detection sensor 71 detects the voltage Vb between the first converter 55 and the switching device 59 and outputs the detection result to the control unit 51. The current detection sensor 70 and the voltage detection sensor 71 correspond to current voltage detection means and effective capacity detection means.

  Based on voltage Vb detected by voltage detection sensor 71, control unit 51 calculates SOC (State Of Charge), which is an index indicating the remaining battery rate. Specifically, assuming that the voltage Vb of the first to fourth batteries 61 to 64 at the time of full charge is the reference voltage Vm, the SOC is calculated as “(detection voltage Vb / reference voltage Vm) × 100” as a percentage. Therefore, as shown in the graph of FIG. 3, there is a proportional relationship between the voltage Vb and the SOC, and the SOC also decreases as the voltage Vb decreases.

  By the way, the battery generally deteriorates with the passage of time. As the battery deteriorates, the effective capacity of the battery decreases. For example, a new battery can store a maximum amount of power of 100 Wh, whereas a deteriorated battery of the same type as that of the new battery has an effective capacity reduced by 20 Wh and can store only a maximum amount of power of 80 Wh. Therefore, for example, when the first to fourth batteries 61 to 64 are deteriorated, there is a possibility that a sufficient amount of power for emergency use cannot be stored even in the fully charged state.

  Therefore, the control unit 51 executes an emergency power securing program every predetermined cycle (for example, every month). The program is executed according to the processing procedure shown in the flowchart of FIG.

  First, the control unit 51 sets the first to fourth batteries 61 to 64 that have consumed power by natural discharge or the like through the second converter 56 to a fully charged state (S101). And the control part 51 starts the discharge of the 1st-4th batteries 61-64 used as the fully charged state through the 1st converter 55 (S102). At this time, the control unit 51 starts measuring the time T required for discharging the first to fourth batteries 61 to 64 through the timer 51b, and measures the current I1 and the voltage Vb through the current detection sensor 70 and the voltage detection sensor 71. To start.

  That is, as shown in the graph of FIG. 3, the voltage Vb of the first to fourth batteries 61 to 64 gradually decreases by discharging from 4.2 V at the time of full charge. And the control part 51 stops discharge, when the voltage Vb becomes below the voltage threshold value Va (it is YES at S103) (S104). At this time, the control unit 51 ends the measurement of the time T, the current I1, and the voltage Vb. In this example, the voltage threshold Va is set to 3.6 V, and the SOC of the first to fourth batteries 61 to 64 is 50 when the voltage Vb becomes the voltage threshold Va. %.

  And the control part 51 calculates the discharge amount Pout of the 1st-4th batteries 61-64 by the product of the said each measured time T, the electric current I1, and the voltage Vb (S105). Further, the control unit 51 compares the discharge amount Pout with a preset discharge threshold Pa (S106). Here, the discharge amount Pout is a value corresponding to the effective capacities of the first to fourth batteries 61 to 64. For example, when the SOC is changed from 100% to 50%, the discharge amount from a battery with an effective capacity of 100 Wh is 50 Wh, whereas the discharge amount from a battery with an effective capacity of 80 Wh is 40 Wh. Therefore, the effective capacities of the first to fourth batteries 61 to 64 can be estimated from the discharge amount Pout when the SOC is changed from 100% to 50%. Based on this, the discharge threshold Pa is set so that the effective capacities of the first to fourth batteries 61 to 64 are equal to or greater than the amount of power required in an emergency.

  When the discharge amount Pout becomes less than the discharge threshold Pa (YES in S106), the control unit 51 adds the fifth battery 65 to the emergency first to fourth batteries 61 to 64 through the switching device 59. (S107). As a result, the effective capacities of the first to fifth batteries 61 to 65 are increased, and the first to fifth batteries 61 to 65 can store the amount of power required in an emergency. In this case, the sixth to eighth batteries 66 to 68 are used for normal use, and the first to fifth batteries 61 to 65 are used for emergency use. Note that the next emergency power securing program is executed for the first to fifth batteries 61 to 65 as emergency and the sixth to eighth batteries 66 to 68 as normal.

  On the other hand, when the discharge amount Pout becomes equal to or greater than the discharge threshold Pa (NO in S106), it is possible to store the amount of power required in an emergency with the effective capacity of the emergency first to fourth batteries 61 to 64. To finish the process.

As described above, according to the embodiment described above, the following effects can be obtained.
(1) When it is determined that the effective capacity of the emergency first to fourth batteries 61 to 64 is insufficient due to deterioration or the like, the normal fifth battery 65 is used as the emergency first to fourth batteries 61. Added to ~ 64. As a result, the effective capacity of the emergency battery can be increased by the effective capacity of the fifth battery 65, and a sufficient amount of power can be secured during a power failure.

  (2) The discharge amount is calculated based on the current I1 and the battery voltage Vb of the emergency first to fourth batteries 61 to 64 detected by the current detection sensor 70 and the voltage detection sensor 71. Here, as the effective battery capacity of the battery decreases due to deterioration, the discharge amount of the battery decreases. Therefore, based on the comparison between the discharge amount Pout of the emergency first to fourth batteries 61 to 64 and the discharge threshold Pa, whether or not the effective capacity of the first to fourth batteries 61 to 64 is sufficient. Judgment is possible. Here, the discharge threshold value Pa is set based on the amount of discharge when discharged with an effective capacity required at the time of a power failure. That is, when the discharge amount Pout of the emergency first to fourth batteries 61 to 64 is less than the discharge threshold Pa, it is determined that the effective capacities of the first to fourth batteries 61 to 64 are insufficient. Automatically, the number of emergency batteries is increased. Thereby, the effective capacity | capacitance of an emergency battery can be increased and sufficient electric energy can be ensured at the time of a power failure.

  (3) In order to increase the effective capacity of the first to fourth batteries 61 to 64 for emergency use, the fifth battery 65 for normal use may be assigned for emergency use. Control such as increasing the proportion used for the battery is unnecessary. Therefore, by providing a large number of batteries, the effective capacities of the emergency first to fourth batteries 61 to 64 can be increased more easily.

In addition, the said embodiment can be implemented with the following forms which changed this suitably.
In the above embodiment, the discharge amount Pout of the first to fourth batteries 61 to 64 is calculated. However, the processes shown in S101 to S105 of FIG. The discharge amount Pout of the first to fourth batteries 61 to 64 may be calculated by adding Pout. In this case, the batteries 61 to 68 need to be connected in parallel to both the converters 55 and 56, and the current detection sensor 70 and the voltage detection sensor 71 must be provided between the first to eighth batteries 61 to 68 and the switching device 59.

  According to this configuration, the effective capacities of the first to eighth batteries 61 to 68 can be determined. Therefore, for example, the emergency first battery 61 that has deteriorated and the normal eighth battery 68 that has not deteriorated are replaced, the first battery 61 is used as normal, and the eighth battery 68 is used as emergency. By doing so, it is possible to secure an effective capacity as much as necessary in an emergency without excessively reducing the effective capacity of the battery for normal use.

  In the above embodiment, the current detection sensor 70 and the voltage detection sensor 71 are provided separately from the first converter 55, but the current detection sensor 70 and the voltage detection sensor 71 are built in the first converter 55. Also good.

  In the above embodiment, in the initial setting, the first to fourth batteries 61 to 64 are assigned for emergency use, and the fifth to eighth batteries 65 to 68 are assigned for normal use. However, the total number of batteries and the number of batteries allocated for emergency and normal use are not limited to this.

  In the above embodiment, the fifth battery 65 is added to the emergency first to fourth batteries 61 to 64 when the discharge amount Pout is less than the discharge threshold Pa. However, the number of added batteries is not limited to one, and a plurality of batteries may be added. In this case, for example, when the fifth battery 65 is added for emergency use, the processes according to steps S101 to S106 in FIG. 4 are performed again, and the effective capacities of the first to fifth batteries 61 to 65 are required in an emergency. It is determined whether or not only as much as is secured. When the discharge amount Pout is still less than the discharge threshold value Pa (YES in step S106), an effective capacity required in an emergency is not secured, and a sixth battery 66 is added for emergency use. To do. As a result, the effective capacity required in an emergency can be ensured more reliably.

  In the above embodiment, the time T until the voltage Vb (4.2 V) at full charge reaches the voltage threshold Va (3.6 V) is measured. Here, the voltage threshold Va is not limited to 3.6 V. For example, by setting the voltage threshold Va to a value close to 4.2 V, the discharge shown in step S104 in FIG. 4 is stopped in a shorter time. It is possible to proceed to the process, and it can be expected that the emergency power securing program process is accelerated. Moreover, since the detection time of the current I1 and the voltage Vb is extended by setting the voltage threshold value Va to a smaller value, the discharge amount Pout can be calculated with higher accuracy.

  In the above embodiment, the effective capacity can be estimated based on the discharge amount Pout of the first to fourth batteries 61 to 64, but the effective capacity can also be estimated based on the charge amount. In this case, for example, the effective capacities of the first to fourth batteries 61 to 64 are estimated based on the amount of charge until the voltage Vb is changed from 3.6 V to 4.2 V.

  In the above embodiment, the effective capacity is estimated based on the discharge amount Pout. However, it is also possible to estimate the effective capacity based on the time T required for discharge. Specifically, as the battery deteriorates, the voltage Vb drops faster even when the battery is discharged by the same amount of power. Here, as shown in steps S103 and S104 of FIG. 4, the measurement of the time T required for discharging ends when the voltage Vb becomes equal to or lower than the voltage threshold value Va. Therefore, as the first to fourth batteries 61 to 64 deteriorate, the time T required for discharging becomes shorter. Therefore, the degree of deterioration of the first to fourth batteries 61 to 64, and hence the effective capacity of the first to fourth batteries 61 to 64 can be estimated based on the time T required for discharging.

  DESCRIPTION OF SYMBOLS 1 ... Power distribution system, 2 ... Commercial alternating current power supply (AC power supply), 3 ... Solar cell, 4 ... Fuel cell, 7 ... Control unit, 12 ... Cross flow connection line, 13-15 ... DC system power line, 16 ... Battery unit ( (Battery control unit), 51 ... control unit, 51a ... memory, 51b ... timer, 53 ... solar battery converter, 55 ... first converter, 56 ... second converter, 58 ... bidirectional converter, 59 ... switching device, 61-68 ... 1st-8th battery, 70 ... Current detection sensor, 71 ... Voltage detection sensor 71.

Claims (2)

A plurality of batteries supplying power to the electrical load;
A battery comprising: a control unit that controls discharging and charging of the plurality of batteries and that allocates the plurality of batteries as a normal battery group that is used in a normal state and an emergency battery group that is used in a power failure. In the control unit,
An effective capacity detecting means for detecting an effective capacity of the emergency battery group,
The effective capacity detection means calculates a discharge amount at a timing when a predetermined battery remaining rate is reached with respect to a fully charged state for the emergency battery group, and based on the battery remaining rate and the discharge amount And detecting the effective capacity of the emergency battery group, and the control unit automatically determines that the effective capacity of the emergency battery group is insufficient based on the detection result of the effective capacity detection means. A battery control unit for increasing the number of batteries allocated for emergency use in The battery control unit according to claim 1,
The effective capacity detection means is a current voltage detection means for detecting a discharge current and a battery voltage of the emergency battery group,
When the emergency battery group is discharged at a predetermined timing, the control unit calculates a discharge amount based on a detection result of the current-voltage detection means, and the calculated discharge amount is required at the time of a power failure. Determining that the effective capacity of the emergency battery group is insufficient, when the discharge threshold is less than the discharge threshold set based on the discharge amount when discharged at the effective capacity of the battery group, A battery control unit for automatically increasing the number of batteries allocated for emergency use.

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