JP2007322398A - Battery pack and method for detecting fully-charge capacity - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically detect a full charge capacity, according to the state of deterioration. <P>SOLUTION: The voltage, temperature, externally connected discharge load of a secondary battery are detected for each predetermined time. Moreover, when a predetermined amount is discharged, capacity retention ratio indicative of the proportion of a current battery capacity to an initial battery capacity stored, in advance, in a storage section is calculated, according to the detected voltage of the secondary battery by using a predetermined linear approximation formula. Furthermore, a full charge capacity indicative of a maximum battery capacity by which the secondary battery can be charged is calculated, according to the capacity retention ratio thus calculated and the initial battery capacity. The full charge capacity calculated is stored in the storage section. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a battery pack for detecting a full charge capacity corresponding to a deteriorated state and a full charge capacity detection method.

  In recent years, secondary batteries are widely used in various electronic devices, and in these electronic devices, information such as the remaining capacity of the secondary battery and the usable time can be displayed on a display area such as a screen. The display of remaining capacity and available time is a guideline for using electronic devices, but it is especially useful for electronic devices used for business purposes such as broadcasting devices to prevent them from becoming unusable during coverage. Therefore, accurate display is required.

  Such information such as remaining capacity and usable time is calculated using a predetermined calculation method based on the full charge capacity of the secondary battery. However, the secondary battery deteriorates as it is used, and the full charge capacity decreases. Therefore, if the remaining capacity and usable time are always calculated based on the full charge capacity of the secondary battery when it is new, an error will occur in the display of the remaining capacity and usable time as the secondary battery is used. Will occur.

  Therefore, in a conventional secondary battery, data is obtained by conducting a test in advance as to how much the capacity of the battery cell deteriorates as the number of times of charge and cycle count progresses, and the number of times of charge and cycle count are calculated based on the data. The full charge capacity is updated accordingly. Then, the remaining capacity and usable time are calculated based on the updated full charge capacity. By doing so, errors in the remaining capacity and the usable time can be reduced as compared with the conventional case.

  However, since the degree of deterioration of the secondary battery varies depending on the user's usage frequency, environmental conditions, load conditions, etc., the accurate full charge capacity can be calculated only by the number of times of charging and the cycle count using the above method. It is difficult.

  In addition, there is a method of measuring the full charge capacity accurately by discharging until the remaining capacity of the secondary battery becomes 0, and then setting the secondary battery to a fully charged state. However, in this case, the user needs to intentionally discharge and charge the secondary battery. Further, since it takes time to discharge and charge the secondary battery, it takes time to calculate the full charge capacity.

  In order to solve such problems, an assembled battery is temporarily put into a resting state, then discharged or charged for a short time with a constant current, and the internal resistance is obtained from the change in the terminal voltage before and after the discharging or charging. A method for estimating the full charge capacity based on the resistance value is described in Patent Document 1 below.

JP 2000-67932 A

  However, in the method for estimating the full charge capacity described in Patent Document 1 described above, there is a problem that it is necessary to perform charge / discharge even for a short time, which is troublesome. In addition, it is necessary to provide a special circuit or the like in order to estimate the full charge capacity of the secondary battery, and there is a problem that the cost for manufacturing the secondary battery increases.

  Accordingly, an object of the present invention is to provide a battery pack and a full charge capacity detection method capable of automatically calculating a full charge capacity in accordance with a deterioration state.

  In order to solve the above-described problem, a first invention is a battery pack of a secondary battery, and a detection unit that detects a voltage, a temperature of the secondary battery, and an externally connected discharge load every predetermined time; When a predetermined amount is discharged, a capacity retention ratio indicating a ratio of the current battery capacity to the initial battery capacity is calculated based on the voltage, and charging in the secondary battery is performed based on the calculated capacity retention ratio and the initial battery capacity. A battery pack comprising: a calculation unit that calculates a full charge capacity indicating a maximum possible battery capacity; and a storage unit that stores an initial battery capacity and stores the calculated full charge capacity.

  The second aspect of the invention also includes a detection step for detecting the voltage and temperature of the secondary battery and a discharge load connected to the outside at predetermined time intervals, and the storage unit stores in advance based on the voltage when discharging a predetermined amount. A capacity retention ratio indicating the ratio of the current battery capacity to the calculated initial battery capacity is calculated, and a full charge indicating a maximum rechargeable battery capacity in the secondary battery is calculated based on the calculated capacity retention ratio and the initial battery capacity. A full charge capacity detection method comprising: a calculation step for calculating a capacity; and a storage step for storing the calculated full charge capacity.

  As described above, according to the first and second aspects of the present invention, when a predetermined amount is discharged, a capacity retention ratio indicating the ratio of the current battery capacity to the initial battery capacity is calculated based on the voltage detected every predetermined time. Since the full charge capacity indicating the maximum battery capacity that can be charged in the secondary battery is calculated based on the calculated capacity retention rate and the initial battery capacity, the full charge capacity is automatically calculated.

  In the present invention, since the full charge capacity is calculated based on the voltage of the secondary battery detected every predetermined time, the full charge capacity is automatically calculated without any special operation by the user. There is an effect that can be.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an exemplary configuration of a battery pack 20 according to an embodiment of the present invention. In the battery pack 20, when the electronic device is used, the positive electrode terminal 1 and the negative electrode terminal 2 are connected to the positive electrode terminal and the negative electrode terminal of the electronic device, respectively, and discharging is performed. In addition, the battery is attached to the charger during charging, and the positive electrode terminal 1 and the negative electrode terminal 2 are connected to the positive electrode terminal and the negative electrode terminal of the charger, respectively, as in the case of using the electric device, and charging is performed.

  The battery pack 20 mainly includes a battery cell 7, a microcomputer 10, a measurement circuit 11, a protection circuit 12, a switch circuit 4, and communication terminals 3a and 3b. The battery cell 7 is, for example, a secondary battery of a lithium ion battery, and one or a plurality of secondary batteries are connected in series.

  The measurement circuit 11 measures the voltage of each battery cell 7 in the battery pack 20 and supplies the measured value to the microcomputer 10. Further, the measurement circuit 11 measures the magnitude and direction of the current using the current detection resistor 9 and sends the measurement value to the microcomputer 10. Furthermore, the measurement circuit 11 also has a function as a regulator that stabilizes the voltage of the battery cell 7 and generates a power supply voltage.

  The microcomputer 10 calculates the full charge capacity of the battery cell 7 based on the voltage value and current value input from the measurement circuit 11 and the battery temperature measured by the temperature detection element 8 such as a thermistor. The calculated full charge capacity value, measured value, and the like are stored in a nonvolatile memory EEPROM (Electrically Erasable and Programmable Read Only Memory) 13. The EEPROM 13 stores in advance a full charge capacity value when not in use as an initial full charge capacity value. Furthermore, the microcomputer 10 measures the voltage value and integrates the current value using the voltage value and the current value input from the measurement circuit 11. A method for detecting the full charge capacity will be described later.

  The protection circuit 12 sends a control signal to the switch circuit 4 when the voltage of any of the battery cells 7 becomes an overcharge detection voltage or when the voltage of the battery cell 7 becomes equal to or lower than the overdischarge detection voltage. This prevents overcharge and overdischarge. Here, in the case of a lithium ion battery, the overcharge detection voltage is determined to be 4.2 V ± 0.5 V, for example, and the overdischarge detection voltage is determined to be 2.4 V ± 0.1 V.

  The switch circuit 4 includes a charge control FET (Field Effect Transistor) 5 and a discharge control FET 6. When the battery voltage becomes the overcharge detection voltage, the charging control FET 5 is turned off and the charging current is controlled not to flow. Note that after the charge control FET 5 is turned off, only discharging is possible through the parasitic diode 5a.

  Further, when the battery voltage becomes the overdischarge detection voltage, the discharge control FET 6 is turned off, and the discharge current is controlled not to flow. Note that after the discharge control FET 6 is turned OFF, only charging is possible through the parasitic diode 6a.

  When the communication terminals 3a and 3b are attached to an electronic device such as a camcorder (camcorder: an abbreviation of camera and recorder), the communication terminals 3a and 3b transmit information on the full charge capacity and the remaining battery capacity to the device. Upon receiving this information, the electronic device displays the full charge capacity, the remaining capacity ratio, the remaining usable time, etc. on a display unit such as a liquid crystal display.

  Next, a full charge capacity detection method in the battery pack 20 according to the embodiment of the present invention will be described. The full charge capacity of the battery pack 20 decreases as the battery cell 7 deteriorates using the battery pack 20. When the battery cell 7 is deteriorated, the battery voltage when a predetermined amount is discharged is lower than the battery voltage of a new battery pack. Further, the battery voltage in this case varies depending on the degree of deterioration of the battery cell 7.

  Therefore, in the embodiment of the present invention, the capacity retention rate of the battery pack 20 is calculated based on the difference in voltage of the battery cell 7 according to the degree of deterioration, and the battery pack 20 is based on the calculated capacity retention ratio. The full charge capacity of was calculated.

  Hereinafter, the full charge capacity detection method will be described in more detail with a specific example. Here, the case where the battery cell 7 which connected the four lithium ion secondary batteries in series is used is demonstrated as an example. The battery voltage and full charge capacity of the battery pack used in this description are 16.8 [V] and 6600 [mAh], respectively, and the voltage at which the remaining amount is 0 is 11000 [mV]. .

  FIG. 2 shows the relationship between the discharge capacity and voltage of the battery pack 20 having different degrees of deterioration. The horizontal axis represents the discharge capacity after charging the battery cell 7 to the full charge capacity, and the vertical axis represents the voltage of the battery cell 7. In addition, this result is a result of measuring each battery pack 20 when the ambient temperature of the battery pack 20 is 25 ° C. and a discharge load of 30 [W] is connected to the battery pack.

  As shown in FIG. 2, the characteristics indicated by reference numerals 31 a to 31 d indicate characteristics of the battery pack having a large degree of deterioration in the order of reference numerals 31 a, 31 b, 31 c, and 31 d, and as the degree of deterioration increases, The voltage value of the battery cell 7 at the time of fixed discharge decreases. Further, the dischargeable capacity from the fully charged state decreases as the degree of deterioration increases. Further, in each battery cell 7, the change in voltage is large with respect to the change in discharge capacity at the end of discharge.

  Thus, it is recognized that the dischargeable capacity from the fully charged state and the voltage value of the battery cell 7 when discharged by a predetermined amount differ depending on the degree of deterioration of the battery cell.

  Based on the results shown in FIG. 2, the relationship between the voltage of the battery cell 7 when a predetermined amount is discharged and the capacity retention rate of the battery pack 20 will be considered. FIG. 3 shows, as an example, the voltage value of the battery cell 7 when each battery cell 7 having a different degree of deterioration is connected with a discharge load of 30 [W] and discharged at 1000 [mAh], and the battery pack 20. The relationship with capacity retention is shown. The horizontal axis indicates the voltage of the battery cell 7, and the vertical axis indicates the capacity retention rate of the battery pack 20.

In this case, as shown in FIG. 3, it is recognized that there is a linear relationship between the voltage of the battery cell 7 and the capacity retention rate. By expressing this linear relationship by an approximate expression, the capacity retention rate of the battery pack 20 can be calculated from the voltage of the battery cell 7. Specifically, for example, the capacity retention rate R ′ [%] when the voltage of the battery cell 7 is V [mV] is calculated based on Expression (1).
R ′ = 0.0451V−609 (1)

  In order to derive an approximate expression showing a linear relationship between the voltage of the battery cell 7 and the capacity retention rate, the case where the discharge capacity from the fully charged state is 1000 [mAh] This is because the change in the voltage of each battery cell 7 with respect to the change in the discharge capacity is large, and the difference in the voltage of each battery cell 7 with respect to the degree of deterioration of the battery pack 20 is small near full charge.

  Further, in this example, the case where the discharge capacity from the fully charged state is 1000 [mAh] has been described so as to derive the approximate expression shown in Expression (1). However, this is not limited to this example. Any region may be used as long as the change in the voltage of the battery cell 7 is small with respect to the change.

  Incidentally, the voltage V of the battery cell 7 varies depending on the temperature of the battery cell 7 and the connected discharge load. Therefore, when the capacity retention rate is calculated using the above mathematical formula (1), there is an error between the calculated capacity retention rate and the actual capacity retention rate depending on the environmental conditions and load conditions in which the battery pack 20 is used. It will occur.

  Therefore, the calculated capacity retention rate is corrected by the temperature and the discharge load, and the capacity retention rate under the standard environmental conditions and load conditions is calculated. By doing so, the capacity retention rate can be calculated more accurately.

  FIG. 4 shows the relationship between the temperature of the battery cell 7 and the capacity retention rate for the battery packs 20 having different degrees of deterioration. The horizontal axis indicates the temperature of the battery cell 7, and the vertical axis indicates the capacity retention rate of the battery pack 20. The characteristics indicated by reference numerals 32a to 32c indicate the characteristics of the battery pack having a large degree of deterioration in the order of reference numerals 32a, 32b, and 32c, and the capacity retention rate decreases as the degree of deterioration increases.

  In this case, as shown in FIG. 4, in each battery pack 20, it is recognized that the capacity retention increases as the temperature of the battery cell 7 increases, and there is a linear relationship. By averaging this linear relationship for each battery pack 20 and expressing it by an approximate expression, a correction value based on the temperature of the battery cell 7 can be calculated.

Specifically, for example, the temperature correction value when the temperature of the battery cell 7 is T ° C. with the temperature of the battery cell 7 being 30 ° C. is calculated based on the formula (2).
Temperature correction value = 1.4 × (30−T [° C.]) (2)

  In this example, it is assumed that the environmental temperature of the battery pack 20 is 25 ° C. and the temperature of the battery cell 7 is 30 ° C. are equivalent temperatures. This is because when the environmental temperature of the battery pack 20 is 25 ° C., the temperature of the battery cell 7 is about 30 ° C. Therefore, in this example, the correction value is calculated based on the case where the temperature of the battery cell 7 is 30 ° C.

  FIG. 5 shows the relationship between the connected discharge load and the capacity retention rate for each battery pack 20 having different degrees of deterioration. The horizontal axis indicates the discharge load connected to the battery pack 20, and the horizontal axis indicates the capacity retention rate of the battery pack 20. The characteristics indicated by reference characters 33a to 33c indicate the characteristics of the battery pack having a large degree of deterioration in the order of reference numerals 33a, 33b, and 33c, and the capacity retention rate decreases as the degree of deterioration increases.

  Further, in this case, as shown in FIG. 5, in each battery pack 20, it is recognized that the capacity retention decreases as the connected discharge load increases, and there is a linear relationship. By averaging this linear relationship for each battery pack 20 and expressing it by an approximate expression, the correction value due to the discharge load of the battery cell 7 can be calculated.

Specifically, for example, the load correction value when the connected discharge load is 30 [W] and the discharge load connected to the battery pack 20 is L [W] is expressed by Equation (3). Calculated based on
Load correction value = 1.7 × (L [W] −30) (3)

The capacity of the battery pack 20 converted when the environmental temperature is 25 ° C. and the discharge load is 30 [W] based on the capacity retention ratio R ′ calculated as described above, the temperature correction value, and the load correction value. The retention rate R is calculated based on Equation (4).
Capacity retention ratio R [%] = R ′ + temperature correction value + load correction value (4)

  In this example, when the capacity retention rate R calculated by the above equation (4) is 100% or more, the capacity retention rate R of the battery pack 20 is 100%, and when the capacity retention rate R is 40% or less. The capacity retention rate R is calculated as 40%.

Therefore, the full charge capacity converted from the capacity retention ratio R and the full charge capacity 6600 [mAh] of the new battery pack 20 when the environmental temperature is 25 ° C. and the discharge load is 30 [W] is expressed by Equation (5). Calculated based on
Full charge capacity [mAh] = 6600 [mAh] × R [%] / 100 (5)

  In the above-described full charge capacity detection method, the environmental temperature ranges from 15 ° C. to 35 ° C. (in the case of the battery cell 7 temperature, from 20 ° C. to 45 ° C.), and the discharge load ranges from 20 [W]. It is preferable to apply to the case of a range up to 50 [W]. This is because the calculation accuracy of the full charge capacity calculated as described above is within ± 15%. Further, by further narrowing these ranges, the accuracy of the calculated full charge capacity can be further increased.

  In this way, the capacity retention rate can be calculated based on the measured voltage of the battery cell 7, and the full charge capacity can be calculated based on the calculated capacity retention rate. Further, when calculating the capacity retention rate, the capacity retention rate is calculated according to the environmental condition and the load condition, so that the accuracy of the calculated full charge capacity can be improved.

  In addition, the numerical value used for the mathematical formula for calculating the full charge capacity is a value that can be applied only when four secondary batteries are connected in series as the battery cell 7, for example, a secondary connected in series. For the battery pack having another configuration in which the number of batteries is different, the above formula can be applied by appropriately changing the numerical value used in the formula.

  Next, a method for detecting the full charge capacity in battery pack 20 according to an embodiment of the present invention will be described. FIG. 6 is a flowchart showing a process flow of the full charge capacity detection method in microcomputer 10 in battery pack 20 according to the embodiment of the present invention. Here, it is assumed that measurement of voltage, charge / discharge current, battery temperature, and calculation of remaining capacity are continuously performed, and the processing of the flowchart of FIG. 6 is repeated cyclically at predetermined time intervals. . For example, the process of the flowchart of FIG. 6 is repeated every predetermined time. The process of this flowchart is preferably repeated every 250 ms, which is the timing for calculating the remaining capacity, for example.

  In step S <b> 1, the measurement circuit 11 measures the voltage and charge / discharge current of each cell of the battery cell 7 and supplies it to the microcomputer 10. Further, the battery temperature detected by the temperature detection element 8 is supplied to the microcomputer 10.

  Next, in step S2, the microcomputer 10 calculates the remaining capacity of the battery pack 20 based on the voltage, charge / discharge current, and battery temperature measured in step S1. A method for detecting the remaining capacity will be described later.

  In step S3, the microcomputer 10 determines whether or not the battery pack 20 is being discharged. As a result of the determination, if it is determined that the battery pack 20 is being discharged, the process proceeds to step S4. If it is determined that the battery pack 20 is not being discharged, the process proceeds to step S1.

  In step S4, the microcomputer 10 determines whether or not 1000 mAh has been discharged from the fully charged state based on the value of the fully charged capacity stored in the EEPROM 13. As a result of the determination, if it is determined that 1000 mAh is discharged, the process proceeds to step S5. If it is determined that 1000 mAh is not discharged, the process proceeds to step S1.

  In step S <b> 5, the microcomputer 10 determines whether or not the temperature of the battery cell 7 is in the range of 19 [° C.] to 45 [° C.] based on the battery temperature supplied from the temperature detection element 8. As a result of the determination, when it is determined that the temperature of the battery cell 7 is in the range of 19 [° C.] to 45 [° C.], the process proceeds to step S6 and the temperature of the battery cell 7 is changed from 19 [° C.] to 45 [° C.]. If it is determined that the temperature is not within the range of [° C.], the process proceeds to step S1.

  In step S6, the microcomputer 10 determines whether or not the discharge load connected to the battery pack 20 is in the range of 20 [W] to 50 [W]. As a result of the determination, if it is determined that the discharge load is in the range of 20 [W] to 50 [W], the process proceeds to step S7, and the discharge load is not in the range of 20 [W] to 50 [W]. If it is determined, the process proceeds to step S1. The discharge load amount is calculated based on the charge / discharge current and voltage measured by the measurement circuit 11. Specifically, for example, it is calculated by a product of a charge / discharge current value and a voltage value.

  In step S7, the microcomputer 10 calculates the full charge capacity based on the voltage measured in step S1, the temperature of the battery cell 7, and the discharge load. Then, the process proceeds to step S8.

  In step S8, the microcomputer 10 compares the full charge capacity value currently set with the full charge capacity value calculated in step S7, and the difference between the full charge capacity values is ± 990 mAh or more. Judge whether there is. As a result of the determination, if it is determined that the difference in the value of the full charge capacity is ± 990 mAh or more, the process proceeds to step S9, and if it is determined that the difference in the value of the full charge capacity is not more than ± 990 mAh, The process proceeds to step S1.

  In step S8, when the calculated full charge capacity reaches 2640 [mAh], which is a capacity retention rate of 40%, the calculation of the full charge capacity ends.

  In step S9, the microcomputer 10 stores the calculated full charge capacity value in the EEPROM 13 and updates the full charge capacity value. Then, the process returns to step S1.

  Next, a method for detecting the remaining capacity of the battery pack 20 will be schematically described with reference to FIG. The remaining capacity detection method is not directly related to the full charge capacity detection method according to the embodiment of the present invention, and a detailed description thereof will be omitted. Here, as an example, a remaining capacity detection method using an integration method and a voltage method will be described.

  As shown in FIG. 7, at the start of discharge, the remaining capacity rate by the integration method is used and gradually changed to the remaining capacity rate by the voltage method. In addition, the remaining capacity ratio is detected by the voltage method in the vicinity of the end of the discharge, and when the discharge is terminated, the cut-off voltage and the remaining capacity ratio of 0% are surely matched to completely switch to the voltage method. ing.

  Switching between the voltage method and the integration method (current integration or voltage integration) when detecting the remaining capacity ratio is called the voltage method reliability. It is performed based on a parameter for determining whether to use for the above. Then, according to the voltage method reliability, the final remaining capacity rate is obtained by weighted addition of the remaining capacity rate obtained by the voltage method and the remaining capacity rate obtained by the integration method. By such weighted addition using the voltage method remaining capacity ratio, stable detection is performed without the remaining capacity ratio changing rapidly.

  In the above description, the method for using the integration method and the voltage method together has been described as the method for detecting the remaining capacity of the battery pack 20, but this is not limited to this example. For example, the remaining capacity of the battery pack 20 may be calculated only by the integration method or the voltage method.

  As described above, in the embodiment of the present invention, the capacity retention rate of the battery pack 20 is calculated based on the voltage of the battery cell 7 automatically measured every predetermined time, and the calculated capacity retention rate is obtained. Based on this, the full charge capacity is calculated. Therefore, the full charge capacity of the battery pack 20 can be calculated automatically without the user performing a special operation.

  Moreover, since the capacity retention rate is corrected based on the temperature of the battery cell 7 and the discharge load connected to the battery pack 20 when calculating the capacity retention rate, the error of the calculated full charge capacity is reduced. Thus, the accuracy can be further increased.

  Furthermore, since the full charge capacity is updated every predetermined time, it is possible to prevent problems such as the battery pack becoming insufficient and the electronic device being unable to be used when using the electronic device. it can.

  Furthermore, when the remaining capacity of the battery pack 20 is detected, the full charge capacity is calculated based on the voltage of the battery cell 7 measured every predetermined time, so that the full charge capacity is calculated. There is no need to provide a special circuit.

  In addition, the full charge capacity calculated via the communication terminals 3a and 3b is transmitted to the electronic device side so that the full charge capacity can be displayed on the electronic device side. The deterioration state of the battery pack 20 can be determined.

  Furthermore, since the full charge capacity is updated according to the degree of deterioration of the battery cell 7, an error between the full charge capacity of the battery pack and the full charge capacity displayed on the electronic device or the like can be reduced. It is possible to easily determine whether the battery pack is out of order or has a lifetime.

  The embodiment of the present invention has been described above. However, the present invention is not limited to the embodiment of the present invention described above, and various modifications and applications can be made without departing from the gist of the present invention. Is possible. For example, the numerical values given in the above-described embodiment are merely examples, and different numerical values may be used as necessary.

It is a block diagram which shows the structure of an example of the battery pack by one Embodiment of this invention. It is a basic diagram which shows the relationship between the discharge capacity and voltage of a battery pack from which the degree of deterioration differs. It is a basic diagram which shows the relationship between the voltage value at the time of discharging 1000 mAh of a battery cell, and the capacity retention of each battery pack. It is a basic diagram which shows the relationship between the temperature in a battery pack, and capacity | capacitance retention. It is a basic diagram which shows the relationship between the discharge load connected and a capacity | capacitance retention. It is a flowchart which shows the flow of a process of the detection method of the full charge capacity in the battery pack by one Embodiment of this invention. It is a basic diagram which shows the detection method of remaining capacity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive terminal 2 Negative terminal 3a, 3b Communication terminal 4 Switch circuit 5a, 6a Parasitic diode 5 Charge control FET
6 Discharge control FET
7 Battery cell 8 Temperature detection element 9 Current detection resistor 10 Microcomputer 11 Measurement circuit 12 Protection circuit 13 EEPROM
20 Battery pack

Claims (8)

A secondary battery pack,
A detection unit for detecting the voltage, temperature and discharge load connected to the outside of the secondary battery every predetermined time;
When a predetermined amount is discharged, a capacity retention ratio indicating a ratio of a current battery capacity to an initial battery capacity is calculated based on the voltage, and the secondary capacity is calculated based on the calculated capacity retention ratio and the initial battery capacity. A calculation unit for calculating a full charge capacity indicating a maximum chargeable battery capacity in the battery;
A battery pack that stores the initial battery capacity and a storage unit that stores the calculated full charge capacity. The battery pack according to claim 1,
The arithmetic unit is
A battery pack, wherein the full charge capacity is calculated by correcting the capacity retention rate based on the temperature of the secondary battery. The battery pack according to claim 1,
The arithmetic unit is
A battery pack, wherein the full charge capacity is calculated by correcting the capacity retention rate based on a discharge amount with respect to the discharge load. The battery pack according to claim 1,
The storage unit
A battery pack, wherein the calculated full charge capacity is stored when the full charge capacity calculated by the calculation unit is equal to or greater than a predetermined ratio compared to the initial full charge capacity. The battery pack according to claim 1,
The storage unit
Storing the calculated full charge capacity when the full charge capacity calculated by the arithmetic unit is within a predetermined ratio with respect to the full charge capacity stored in the storage unit; Battery pack to play. The battery pack according to claim 1,
The arithmetic unit is
The battery pack, wherein the full charge capacity is calculated when the temperature detected by the detection unit is within a predetermined range. The battery pack according to claim 1,
The arithmetic unit is
The battery pack, wherein the full charge capacity is calculated when a discharge load detected by the detection unit is within a predetermined range. A detection step of detecting the voltage, temperature and discharge load connected to the outside of the secondary battery every predetermined time;
When a predetermined amount is discharged, a capacity retention ratio indicating the ratio of the current battery capacity to the initial battery capacity stored in the storage unit in advance is calculated based on the voltage, and the calculated capacity retention ratio and the initial capacity A calculation step of calculating a full charge capacity indicating a maximum rechargeable battery capacity in the secondary battery based on the battery capacity;
And a storage step for storing the calculated full charge capacity.

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