JP2012133903A - Battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery pack capable of preventing the exchange of a secondary battery by an illegal recycling manufacturer.SOLUTION: A control circuit includes a removal detection part for outputting each voltage of a secondary battery and outputting abnormal voltage when the secondary battery is removed, a voltage detection part for detecting the voltage from the removal detection part, a state change detection part for detecting the change of voltage state from the voltage detection part, a storage part for storing state change history data showing the change of state when abnormal voltage of the secondary battery is detected by the state change detection part, and a state control unit for setting the battery pack to an inhibited state when state change history data is written in the storage part and setting the battery pack in an available state when the state change history data is not written in the storage part. Thus the battery pack is set in an unavailable state when the secondary battery is removed, so that when the secondary battery is illegally removed and exchanged, a cause of failure or trouble in an external device due to the secondary battery can be eliminated.

Description

  The present invention relates to a battery pack including a secondary battery.

  2. Description of the Related Art In recent years, battery packs that are widely used in electric appliances such as notebook computers and mobile phones include a control circuit that monitors the state of a secondary battery and protects the secondary battery from overcharge and overdischarge. Here, the battery pack cannot be used when the secondary battery reaches the end of its life, but the control circuit often does not reach the end of its life. Therefore, the quality of the battery protection function of the circuit protection board included in the used battery pack is determined. If the protection circuit board has the battery protection function, a new secondary battery is inserted into the protection circuit board. A technique for attaching and recycling the battery pack is known (see, for example, Patent Document 1).

  However, there are many unauthorized recyclers who replace the secondary battery without permission from the manufacturer of the battery pack, and when the battery pack is replaced by such a supplier, there is a high possibility that a bad secondary battery will be installed, There is a problem that bad battery packs are distributed in the market. Further, when such a bad battery pack flows out to the market, the manufacturer of the battery pack suffers a great deal of damage.

  Therefore, the terminal voltage of the secondary battery is monitored using a microcomputer, and if the terminal voltage reaches a set voltage that is set below the lower limit of the voltage range used in normal use, history data is stored in the nonvolatile memory. There is known a technique that allows a secondary battery to be used only when history data is stored in a nonvolatile memory when the microcomputer is restarted (for example, a patent) Reference 2). In this case, if the secondary battery is removed for replacement before the secondary battery is discharged and the terminal voltage falls below the set voltage, the microcomputer stops operating because the power supply voltage for operating the microcomputer is not supplied. However, the history data is not stored in the nonvolatile memory. Therefore, when the secondary battery is attached again and the microcomputer is activated, the history data is not stored in the non-volatile memory, so that the use of the secondary battery is prohibited.

JP 2003-92152 A JP 2007-128674 A

  However, the technique described in Patent Document 2 cannot detect that the microcomputer has been started and stopped by EMI (Electro-Magnetic Interference) or the like. In such a case, the secondary battery is not illegally removed, but it is determined that the battery pack is illegally recycled. For this reason, there is a concern that it may be inconvenient for the user.

  The present invention has been made in view of such circumstances, and determines whether the microcomputer is started or stopped when the secondary battery is removed and the microcomputer is started or stopped due to noise such as EMI. An object of the present invention is to provide a battery pack that can detect whether or not the operation has been performed.

  In order to solve the conventional problems, the battery pack of the present invention is a battery pack including a plurality of secondary batteries and a control circuit, and the control circuit outputs each voltage of the secondary battery, and the secondary battery A removal detection unit that outputs an abnormal voltage when the battery is removed, a voltage detection unit that detects a voltage from the removal detection unit, a state change detection unit that detects a change in the voltage state from the voltage detection unit, and When the state change detection unit detects an abnormal voltage of the secondary battery, the storage unit stores state change history data indicating that the state has changed, and the state change history data is written in the storage unit The battery pack is in a use-prohibited state, and when the state change history data is not written in the storage unit, the battery pack includes a state control unit that makes the battery pack usable, and when the secondary battery is removed, pack To use impossible state.

  With this configuration, when the secondary battery is illegally removed and replaced, the cause of the malfunction or failure of the external device due to the secondary battery can be removed.

  According to the battery pack of the present invention, replacement of the secondary battery by an unauthorized recycler can be prevented. In addition, it is possible to prevent detection of unauthorized recycling with respect to unexpected start and stop of the microcomputer due to noise such as EMI.

1 is a block diagram of a battery pack according to Embodiment 1 of the present invention. It is the flowchart which showed the process in which a battery pack writes lower limit voltage history data. It is a flowchart which shows a process when a power supply circuit starts operation. It is a flowchart which shows the process which an external connection device determines the presence or absence of lower limit voltage log | history data. 6 is a block diagram of a battery pack according to Embodiment 2. FIG. It is the flowchart which showed the process at the time of the operation start of a battery pack. It is a flowchart which shows the process which the battery pack determines the presence or absence of start history data.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of a battery pack 1 according to Embodiment 1 of the present invention. The battery pack 1 includes a control circuit 2, a secondary battery block 3, a power supply circuit 4, terminals T1 and T2, a communication terminal T5, and diodes D1 and D2. The terminals T1 and T2 and the communication terminal T5 are connected to the terminals T3 and T4 and the communication terminal T6 of the external connection device 100, respectively, whereby the external connection device 100 and the battery pack 1 are electrically connected.

  The terminals T1 and T2 are charge / discharge terminals, and the communication terminal T5 is a terminal for transmitting and receiving various data to and from the external connection device 100. The diode D1 has an anode connected to the energization switch 21 and a cathode connected to the power supply circuit 4. The diode D2 has an anode connected to the terminal T1 and a cathode connected to the power supply circuit 4.

  The secondary battery block 3 includes three battery cells 31 to 33 connected in series. The battery cells 31 to 33 are composed of secondary batteries such as a lithium ion secondary battery, a fuel battery, and a nickel cadmium secondary battery. In addition, the number of the battery cells which comprise the secondary battery block 3 is not limited to three, You may comprise from four or more battery cells, You may comprise from two battery cells.

  The control circuit 2 includes an energization switch 21, a calculation unit 22, a storage unit 23, a voltage detection unit 24, a current detection unit 25, a communication unit 26, and a removal detection unit 27. The energization switch 21 is composed of a reversible switch such as an FET or a non-reversible switch such as a thermal fuse, and is turned on or off under the control of the arithmetic unit 22, and in the off state, the secondary battery block 3 and the terminal T1. In the ON state, the secondary battery block 3 and the terminal T1 are electrically connected.

  The voltage detection unit 24 includes an A / D converter and the like, detects a voltage between the terminals of the battery cells 31 to 33, converts the voltage into digital detection data, and outputs the digital detection data to the calculation unit 22. The current detection unit 25 includes a current sensor, is connected between the negative electrode of the secondary battery block 3 and the terminal T2, detects a charging current or a discharging current that is passed through the secondary battery block 3, and calculates detection data. To the unit 22.

  The removal detection unit 27 includes diodes D3 and D4 and R1 and R2. Normally, the voltage detection unit 24 obtains power from the VP. However, for example, when the VP is disconnected to prevent unauthorized recycling, the power source can be acquired from the VM through D3. And while acquiring a power supply from VM, in the voltage detection part 24, the electric potential of VP detects an abnormal voltage by resistance R1. When this abnormal voltage is detected, the data writing unit 222 of the computing unit 22 removes the data into the storage unit 23 and writes history data to recognize that an illegal removal has been performed. The GND of the voltage detection unit 24 is based on VG, and when VG is removed, VL is set to GND of the voltage detection unit 24 via D4. In the voltage detection unit 24, the potential of VG detects an abnormal voltage by the resistor R2. Thus, it is determined that the removal has been performed, and the data writing unit 222 of the calculation unit 22 recognizes that the removal has been performed by writing the history data into the storage unit 23.

  The calculation unit 22 includes a CPU (Central Processing Unit) that executes various processes, a RAM (Random Access Memory) used as a work area of the CPU, and the like, and executes a control program stored in the storage unit 23. To control the battery pack 1. Here, the calculation unit 22 calculates the remaining capacity of the secondary battery block 3 using the voltage of the secondary battery block 3 detected by the voltage detection unit 24 and the current detected by the current detection unit 25. And a function of protecting the secondary battery block 3 from overcharge, overdischarge, and overcurrent.

  In particular, in the present embodiment, the calculation unit 22 includes functions of a state change detection unit 221, a data writing unit 222, a state control unit 223, an operation command determination unit 224, and a data erasure unit 225. These functions are realized by the calculation unit 22 executing the control program written in the storage unit 23.

  The state change detection unit 221 uses the detection data output from the voltage detection unit 24 to confirm that the voltage of at least one battery cell constituting the secondary battery block 3 has become equal to or lower than a predetermined lower limit voltage. This is detected as a change in the state of the battery pack 1. Here, the lower limit voltage is a voltage that is reached when the user does not charge the battery pack for several months at all, and is a voltage that does not reach when the general user normally uses the battery pack. For example, it can be set to 20% or less of the voltage when the battery cells 31 to 33 are fully charged. Also. The state change detection unit 221 uses the detection data output from the voltage detection unit 24 to detect that the secondary battery block 3 has been removed from the control circuit 2 as a change in the state of the battery pack 1.

  The data writing unit 222 writes the lower limit voltage history data to the storage unit 23 when the state change detection unit 221 detects that the voltage of at least one battery cell is equal to or lower than the lower limit voltage, and the writing process is completed. The power supply circuit 4 outputs a signal for stopping the operation of the battery pack.

  In addition, when the operation of the battery pack 1 is started, the data writing unit 222 writes the lower limit voltage history data to the storage unit 23 when the lower limit voltage history data is not written to the storage unit 23.

  Further, the data writing unit 222 writes the removal history data in the storage unit 23 when the state change detection unit 221 detects that the secondary battery block 3 has been removed from the control circuit 2.

  Further, the data writing unit 222 has been determined by the operation command determination unit 224 that the operation command input using the external connection device 100 is a write command for writing the lower limit voltage history data to the storage unit 23. In this case, the lower limit voltage history data is written in the storage unit 23.

  When the lower limit voltage history data is written in the storage unit 23 or when the removal history data is written, the state control unit 223 turns off the energization switch 21 or stops the operation of the battery pack 1 in the power supply circuit 4. The battery pack 1 is set in a use-prohibited state. In addition, when the lower limit voltage history data is not written in the storage unit 23 and when the removal history is not written, the state control unit 223 turns on the energization switch 21 to make the battery pack 1 usable.

  The operation command determination unit 224 determines whether or not the received operation command is an erasure command for erasing the lower limit voltage history data when the communication unit 26 receives an operation command input by an operator using the external connection device 100. Or a write command for writing the lower limit voltage history data.

  The data erasure unit 225 erases the lower limit voltage history data from the storage unit 23 when the lower limit voltage history data is written in the storage unit 23 when the operation of the power supply circuit 4 is started. When the operation command determination unit 224 determines that the operation command input using the external connection device 100 is an erase command for deleting the lower limit voltage history data, the data deletion unit 225 stores the storage unit 23. Delete the lower limit voltage history data from.

  The communication unit 26 receives various data from the external connection device 100 via the communication terminal T5, and transmits various data to the external connection device 100. Specifically, the communication unit 26 transmits data indicating the remaining capacity of the secondary battery block 3 calculated by the calculation unit 22 or receives an operation command input by the operator from the external connection device 100.

  The storage unit 23 includes a rewritable nonvolatile storage device such as an EPROM, stores a control program for controlling the battery pack 1, and lower limit voltage history data written by the data writing unit 222. Memorize etc.

  The power supply circuit 4 stabilizes the power from the secondary battery block 3 or the external connection device 100, supplies the power to the control circuit 2, and operates the battery pack 1. Here, in the power supply circuit 4, the state change detection unit 221 detects that the voltage of at least one battery cell has become equal to or lower than the lower limit voltage, and the data writing unit 222 writes the lower limit voltage history data to the storage unit 23. At that time, the operation is stopped, and the power supplied to the calculation unit 22 is cut off. On the other hand, when the operation of the power supply circuit 4 is stopped, the external connection device 100 is connected, and when a predetermined level of voltage is applied to the terminals T1 and T2, the operation starts and power is supplied to the control circuit 2. To start. The power supply circuit 4 also stops operating when the secondary battery block 3 is removed and power supply to the power supply circuit 4 is stopped, and power supply to the control circuit 2 is stopped.

  Here, the battery pack 1 is generally shipped with the power supply circuit 4 in operation, and the general user also uses the battery pack 1 until at least one battery cell falls below the lower limit voltage. Since this is rare, the operation of the power supply circuit 4 of the battery pack 1 held by a general user rarely occurs.

  The external connection device 100 includes a charging device that charges the secondary battery block 3 or a load device. The external connection device 100 has a communication function, and transmits various data to the battery pack 1 via the communication terminal T6 and receives various data from the battery pack 1. A device such as a notebook personal computer, a mobile phone, a PDA, or a power tool can be employed as the load device.

  Further, the external connection device 100 includes a control unit 101, an energization switch 102, and an input unit 103. The control unit 101 controls the entire external connection device 100. The energization switch 102 includes a reversible switch such as an FET or a non-reversible switch such as a thermal fuse, and is turned on or off under the control of the control unit 101. The input unit 103 receives a write command from the operator for writing the lower limit voltage history data in the storage unit 23 or an erase command from the operator for deleting.

  In the present embodiment, the terminals T1 and T2, the communication terminal T5, and the communication unit 26 correspond to an example of a reception unit.

  Next, the writing process of the lower limit voltage history data by the battery pack 1 of the first embodiment will be described with reference to the flowchart of FIG. First, in step S1, the state change detection unit 221 checks whether the voltage of at least one battery cell constituting the secondary battery block 3 has become equal to or lower than a predetermined lower limit voltage (step S1). When it is detected in step S1 that the voltage is equal to or lower than the predetermined lower limit voltage (YES in step S1), the data writing unit 222 writes the lower limit voltage history data in the storage unit 23 (step S2). On the other hand, in step S1, when the state change detection unit 221 does not detect that the voltage of at least one battery cell constituting the secondary battery block 3 is equal to or lower than the lower limit voltage (NO in step S1), the process is performed. Return to S1.

  Then, the data writing unit 222 outputs a signal instructing the power supply circuit 4 to stop the operation of the battery pack 1, and the power supply circuit 4 stops the operation and stops the power supply to the control circuit 2. (Step S3).

  Next, the removal history data writing process by the battery pack 1 of the first embodiment will be described with reference to the flowchart of FIG. First, the state change detection unit 221 confirms whether any of the battery cells 31 to 33 of the secondary battery block 3 has been removed from the control circuit 2 (step S11). Here, the state change detection unit 221 uses the detection data output from the voltage detection unit 24, and the voltage of at least one battery cell constituting the secondary battery block 3 is equal to or lower than a predetermined lower limit voltage. Thus, it is detected that the battery cell has been removed. In step S11, when it is detected that any of the battery cells has been removed (YES in step S11), the data writing unit 222 writes the removal history data in the storage unit 23 (step S12). On the other hand, when the state change detection unit 221 does not detect that the secondary battery block 3 has been removed from the control circuit 2 in step S11 (NO in step S11), the process returns to step S11.

  Next, processing at the start of operation of the power supply circuit 4 will be described with reference to FIG. It is assumed that the power supply circuit 4 has stopped operating before the processing of this flowchart is executed. First, when the terminals T3 and T4 and the communication terminal T6 of the external connection device 100 are connected to the terminals T1 and T2 and the communication terminal T5 and a voltage of a predetermined level or higher is applied to the power supply circuit 4, the power supply circuit 4 starts operation. Then, power supply to the control circuit 2 is started (step S21).

  The data writing unit 222 or the data erasing unit 225 determines whether or not the lower limit voltage history data is stored in the storage unit 23 (step S22), and the removal history data is stored in the data writing unit 222 or the storage unit 23. It is determined whether or not (step S23). Then, it is confirmed whether or not the lower limit voltage history data is stored in the storage unit 23 (step S24). If the lower limit voltage history data is stored in step S24 (YES in step S24), the data erasing unit 225 sets the lower limit stored in the storage unit 23 in order to make the secondary battery block 3 usable. The voltage history data is erased (step S25).

  Since the lower limit voltage history data and the removal history data are not written in the storage unit 23, the state control unit 223 turns on the energization switch 21 to make the battery pack 1 usable (step S26). Here, for example, the state control unit 223 determines whether or not the lower limit voltage history data is written in the storage unit 23 at regular intervals.

  In step S24, when the lower limit voltage history data is not stored in the storage unit 23 (NO in step S24), it is confirmed whether the removal history data is stored in the storage unit 23 (step S27). If the removal history data is not stored in step S27 (YES in step S27), the data writing unit 222 writes the lower limit voltage history data to the storage unit 23 (step S28). Since the lower limit voltage history data is written in the storage unit 23, the state control unit 223 turns off the energization switch 21 and puts the battery pack 1 in a use-prohibited state (step S29). Here, the state control unit 223 may place the battery pack 1 in a use-prohibited state by causing the power supply circuit 4 to stop the operation of the battery pack 1. In step S27, if the removal history data is not stored in the storage unit 23 (NO in step S27), it is determined that the secondary battery block 3 has not been illegally removed from the control circuit 2, and the battery pack 1 is removed. Make it available.

  As described above, according to the battery pack 1 of the first embodiment, the voltage of any one of the battery cells 31 to 33 constituting the secondary battery block 3 becomes lower than the lower limit voltage, and the operation of the battery pack 1 is performed. Is stopped, the data writing unit 222 writes the lower limit voltage history data in the storage unit 23. Further, when the control circuit 2 is removed from the secondary battery block 3, it is detected, and the data writing unit 222 writes the removal history data to the storage unit 23.

  Therefore, when the secondary battery block 3 is removed from the battery pack 1 before any voltage of the battery cells 31 to 33 becomes lower than the lower limit voltage, the lower limit voltage history data is not written in the storage unit 23. The power supply circuit 4 stops operating. In addition, the removal detection unit detects that the secondary battery block 3 has been removed from the control circuit 2, and the removal history data is stored in the storage unit 23.

  When the operation of the power supply circuit 4 is started, when the lower limit voltage history data is not written in the storage unit 23 and the removal history data is written in the storage unit 23, the data writing unit 222 Then, the lower limit voltage history data is written in the storage unit 23, and the secondary battery block 3 is disabled.

  On the other hand, when the operation of the power supply circuit 4 is started, the battery pack 1 can be used when the lower limit voltage history data is not written in the storage unit 23 and the removal history data is not written in the storage unit 23. Put it in a state.

  When the operation of the power supply circuit 4 is started, if the lower limit voltage history data is written in the storage unit 23, the data erasing unit 225 erases the lower limit voltage history data from the storage unit 23, and the battery pack 1 Is enabled.

  In addition, when the microcomputer stops due to noise such as EMI, the lower limit voltage history data is not written at the next startup, but the removal history data is not written, so the battery pack 1 may be usable. It is possible to avoid malfunctions when unauthorized recycling is not performed.

  The new battery pack 1 is in a use-prohibited state since the lower limit voltage history data is not written. To prevent this, the battery pack 1 is shipped before the new battery pack 1 is shipped. 1 is connected to the external connection device 100, a write command is input from the external connection device 100, the lower limit voltage history data is written to the storage unit 23, and the operation of the power supply circuit 4 is started. Can be shipped.

(Embodiment 2)
Next, the battery pack 1a according to Embodiment 2 will be described. The battery pack 1a according to the second embodiment is characterized in that the start history data is written at the start of operation instead of writing the lower limit voltage history data when the operation is stopped. FIG. 5 shows a block diagram of a battery pack 1a according to the second embodiment. In addition, in the battery pack 1a of Embodiment 2, the same thing as Embodiment 1 attaches | subjects the same code | symbol, and abbreviate | omits description.

  When the external connection device 100 is connected to the state change detection unit 221a, a predetermined voltage is applied to the terminals T1 and T2, the power supply circuit 4 starts operation, and power supply to the control circuit 2 is started. It is determined that the state has changed.

  When the state change detection unit 221a detects the start of operation of the power supply circuit 4, the data writing unit 222a writes start history data indicating that the operation has started in the storage unit 23.

  The data erasure unit 225a erases the start history data from the storage unit 23 when the operation command determination unit 224a determines that the operation command from the operator is an erase command for erasing the start history data.

  When the communication unit 26 receives an operation command input by an operator using the external connection device 100, the operation command determination unit 224a determines whether or not the received operation command is a deletion command for deleting the start history data. Determine.

  Next, the operation of the battery pack 1a according to the second embodiment will be described. FIG. 6 is a flowchart showing processing at the time of starting the battery pack 1a. It is assumed that the operation of the battery pack 1 has been stopped before the processing of this flowchart is executed.

  First, in the state change detection unit 221a, the terminals T3 and T4 and the communication terminal T6 of the external connection device 100 are connected to the terminals T1 and T2 and the communication terminal T5, and power supply to the control circuit 2 is started by the power supply circuit 4. Is detected (step S31).

  The data writing unit 222a writes start history data in the storage unit 23 (step S32). The data erasure unit 225a determines whether or not the operation command transmitted from the external connection device 100 by the operation command determination unit 224a is a deletion command for deleting the start history data (step S33). If it is determined in step S33 that it is an erasure command (YES in step S33), the start history data is erased from the storage unit 23. On the other hand, in step S33, when the communication unit 26 does not receive the start history data deletion command from the external connection device 100 (NO in step S33), the data deletion unit 225a ends the process.

  FIG. 7 is a flowchart showing processing at the start of operation of the power supply circuit 4. First, the state control unit 223 determines whether start history data is written in the storage unit 23 (step S41). If the start history data is written in step S41 (YES in step S41), it is next determined whether or not the removal history data is written in the storage unit 23 (step S42). If the removal history data has been written in step S42 (YES in step S42), the energization switch 21 is turned off and the battery pack 1a is disabled (step S43).

  On the other hand, in step S41, the state control unit 223 determines that the start history data is not written in the storage unit 23 (NO in step S41), or in step S42, the state control unit 223 stores the removal history data in the storage unit 23. If not written (NO in step S42), the energization switch 21 is turned on to make the battery pack 1a usable (step S44).

  As described above, according to the battery pack 1a of the second embodiment, when the secondary battery block 3 is replaced and the operation of the battery pack 1a is started in the recycling process of the battery pack 1a, the storage unit 23 Start history data is written in When the start history data is written in the storage unit 23, the state control unit 223 disables the battery pack 1a, the start history data is not written in the storage unit 23, and the removal history data is written. If it is, the battery pack 1a is put into a usable state.

  Here, the manufacturer of the battery pack 1a gives an instruction to erase the start history data only to an authorized recycler. As a result, the authorized recycler erases the start history data written in the storage unit 23 when the secondary battery block 3 is replaced and the operation of the power supply circuit 4 is started in the recycling process, and the battery pack 1a can be shipped.

  On the other hand, since the unauthorized recycler does not know the erasure command, the battery pack 1a is shipped after erasing the start history data written in the storage unit 23 when the operation of the power supply circuit 4 is started in the recycling process. Can not do it. Therefore, replacement of the secondary battery block 3 by an unauthorized recycler can be prevented.

  Further, when the microcomputer is stopped due to noise such as EMI, even if the start history data is written at the next start-up, the removal history data is not written, so the battery pack 1a can be used. It is possible to avoid malfunctions when unauthorized recycling is not performed.

  According to the present invention, the replacement of the secondary battery block by an unauthorized trader can be prevented, so that a battery pack useful for a device such as a mobile phone or a notebook computer can be provided.

DESCRIPTION OF SYMBOLS 1,1a Battery pack 2 Control circuit 3 Secondary battery block 4 Power supply circuit 21 Energizing switch 22 Operation part 221, 221a State change detection part 222, 222a Data writing part 223 State control part 224, 224a Operation command determination part 225, 225a Data erasure unit 23 Storage unit 24 Voltage detection unit 25 Current detection unit 26 Communication unit 27 Removal detection unit 31, 32, 33 Battery cell 100 External connection device 101 Control unit 102 Power switch 103 Input unit T1, T2, T3, T4 Terminal T5 , T6 communication terminal

Claims (4)

A battery pack comprising a plurality of secondary batteries and a control circuit,
The control circuit includes:
A removal detector that outputs each voltage of the secondary battery and outputs an abnormal voltage when the secondary battery is removed,
A voltage detection unit for detecting a voltage from the removal detection unit;
A state change detector that detects a change in voltage state from the voltage detector;
A storage unit that stores state change history data indicating that the state has changed when an abnormal voltage of the secondary battery is detected by the state change detection unit;
When the state change history data is written in the storage unit, the battery pack is disabled, and when the state change history data is not written in the storage unit, the battery pack is enabled. A battery pack comprising a state control unit. When the voltage of the secondary battery is equal to or lower than the lower limit voltage of the voltage range of the secondary battery during normal use of the battery pack, the state change detection unit writes the storage unit as lower limit voltage history data,
The battery pack according to claim 1, wherein when the history data is written in the storage unit, the state control unit sets the battery pack in a usable state.     2. The battery pack according to claim 1, wherein the removal detection unit includes a parallel circuit of a resistor and a diode in a wiring that the voltage detection unit detects the voltage of the secondary battery.     The state change detection unit records start history data in the storage unit when an external device is connected and power supply to the control circuit is started, and erases the start history data in response to an operation instruction from an operator from the external device. The battery pack according to claim 1.