JPH06153413A - Charge controller and charge control method - Google Patents

Abstract

PURPOSE:To prevent overcharge and besides, display the residual quantity accurately even if the completion of charge can not detected by voltage ripple or temperature change, concerning a charge controller which performs the charge control to a secondary battery. CONSTITUTION:The charge time from charge start to a secondary battery 23 to charge completion is measured actually, and the actual battery capacity is estimated by a substantial capacity computing means 18 from this and the estimated time required for full charge computed based on rated capacity. Moreover, the residual quantity corresponding to the actual battery capacity is computed with a residual quantity computing means 19 and it is displayed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge control device and a charge control method having a function of monitoring the remaining amount of a secondary battery.

With the development of portable computers in recent years,
It is required to extend the operating time by the built-in battery inside the body. Therefore, in order to achieve a longer operating time, it is necessary to have a charging circuit inside the main unit and a function to monitor the remaining battery level. In order to accurately grasp the remaining battery capacity, it is necessary to predict the actual battery capacity, not the rated capacity.

[0003]

Overcharging, when controlling charging, shortens the life of the battery. Therefore, in the conventional charge control device, when a NiCd battery is used, the detection of −ΔV, which detects the completion of charging from the voltage change at the completion of charging, is used as the control means for protecting the battery. When using a Ni-hydrogen battery, ΔT detection is used to detect the completion of charging based on the temperature change at the completion of charging.

In addition, in the case where these cannot be detected, the maximum charging time is determined, and timer control is performed so that charging is not performed for more than that time. In the case of rapid charging in which a current of about 1 C is used, a sufficient change appears to detect −ΔV, ΔT, so −ΔV, ΔT
Is easy to detect, but in the case of long-time charging in which a current of about 0.4 C is charged for a long time, a remarkable change does not appear, so timer control is used.

Further, when controlling the discharge, the consumption current amount is calculated by integrating the discharge current amount, but the remaining amount prediction is inaccurate because the remaining amount is predicted using the rated capacity. .

[0006]

However, in the past, when the charging time was defined, this charging time was constant, and measures were taken against a substantial reduction in capacity due to deterioration of the secondary battery, memory effect, and the like. It wasn't done. Therefore, there is a problem that the life of the secondary battery is shortened by charging for a long time and repeating overcharging.

The present invention prevents the overcharge of the secondary battery and extends the life of the built-in battery by predicting the actual battery capacity from the rated capacity based on the charging time when the charging of the secondary battery is completed. , The purpose is to accurately predict the remaining battery level.

[0008]

FIG. 1 is a diagram for explaining the principle of the present invention. In FIG. 1, 10 is a charge control device for charging a secondary battery, 11 is an external power source such as an AC adapter, and 1
2 is a charging circuit for supplying electricity to the secondary battery, 13 is a voltage detection unit for detecting a voltage change during charging, and 14 is a voltage detection unit.
Is a battery temperature detection unit for detecting a temperature change of the secondary battery during charging, 15 is a charge control microcomputer (microcomputer) for performing charge control, 16 is charging time measuring means, 17 is prediction time calculating means, 18 is a real capacity calculating means, 19 is a remaining amount calculating means for calculating the remaining amount of the secondary battery,
Reference numeral 20 is a remaining amount storage means, 21 is a remaining amount display means for displaying the remaining amount of the secondary battery, 22 is a battery status indicator, 23 is a secondary battery, and 24 is a secondary battery using device such as a portable computer. .

The present invention is provided with a voltage detection unit 13 or a battery temperature detection unit 14 in order to determine the substantial battery capacity of the secondary battery 23. It has a mechanism to detect completion. The charging control microcomputer 15 has the following processing means.

The charging time measuring means 16 is a processing means for measuring the charging time from the start to the completion of charging. The predicted time calculation means 17 is a processing means that predicts the charging time until full charge based on the rated capacity and the charging current of the secondary battery 23. The actual capacity calculation means 18 calculates the measured time obtained by the charging time measurement means 16 and the predicted time calculation means 1
It is a processing means for calculating the actual battery capacity from the estimated time obtained in step 7. From these, the actual battery capacity is predicted from the rated capacity by calculation.

According to the second aspect of the invention, the remaining amount calculation means 1
9, a remaining amount storage means 20, and a remaining amount display means 21 are provided. The remaining amount calculation unit 19 is a processing unit that updates the remaining amount stored in the remaining amount storage unit 20 based on the predicted actual battery capacity based on the charged amount and the discharged amount at the time of charging and discharging. The remaining amount display means 21 is a processing means for controlling the remaining amount of the secondary battery 23 stored in the remaining amount storage means 20 to be displayed on a battery status indicator 22 such as an LCD or an LED.

In the case of the third aspect of the invention, the estimated time calculation means 17 calculates the estimated charge time for the rated charge time minus the charge time for the remaining amount stored in the remaining amount storage means 20. The estimated time is used as the charging time-over time.

According to the fourth aspect of the present invention, the charge control microcomputer 15 has a quick charge processing means for charging with a current of about 1C, a standard charge processing means for charging with a smaller current, and a discharge amount is monitored. Monitoring processing means.

The quick charge processing means performs a quick charge to the secondary battery 23 when the external power supply 11 is connected and the secondary battery using device 24 is not consuming electric power, and at the actual charging time. Based on this, the correction value of the actual capacity with respect to the rated capacity is calculated, and the actual remaining amount of the secondary battery 23 is calculated based on the correction value.

The standard charge processing means is the external power source 11
Is connected and the secondary battery using device 24 is consuming power, the secondary battery 23 is standardly charged, and the actual remaining amount of the secondary battery 23 is calculated based on the correction value. In addition, from the rated charging time and the remaining amount of the secondary battery 23,
Predict the charging time until full charge and stop charging when the charging time is reached.

The monitoring processing means updates the remaining amount of the secondary battery 23 on the basis of the discharge amount when the secondary battery using device 24 is consuming power while the external power source 11 is not connected. .

Further, in the invention according to claim 5, when the external power supply 11 is not connected and the secondary battery using device 24 is not consuming power, the remaining time of the secondary battery 23 from the standby time The amount corresponding to the leak current is subtracted, and the remaining amount stored in the remaining amount storage means 20 is updated.

In a sixth aspect of the invention, when the capacity of the secondary battery 23 to be charged is the rated capacity, the process of calculating the predicted time required to fully charge the battery and the temperature change (Δ
T) or voltage change (−ΔV), when the completion of charging is detected, the process of actually measuring the time required to fully charge the secondary battery 23 and the ratio of the actually measured time and the predicted time for charging , Calculate the correction value for the rated capacity,
Calculating a substantial battery capacity.

[0019]

[Operation] The electric potential of the battery for controlling the charging circuit 12,
It has a means for measuring the temperature of the battery and the like, and is equipped with a charge control microcomputer 15 which takes in the information by using A / D conversion, and has a configuration capable of detecting the completion of charging such as ΔT, −ΔV. From the charging current, the charging time when the battery capacity is the rated capacity can be predicted by the following formula.

Charging time (hours) = Battery capacity (mAh) ÷
Charging current (mA) The time is monitored using the clock of the charging control microcomputer 15, and the actual charging time when the completion of charging is detected by -ΔV, ΔT detection is measured. The actual capacity can be predicted by the following calculation based on the ratio of the predicted time and the actually measured time.

Actual capacity = (measured time ÷ predicted time) × rated capacity That is, in the present invention, the actual capacity of the battery is predicted by calculation by detecting the completion of charging by ΔT, −ΔV. As a result, when ΔT and −ΔV cannot be detected, finer control is possible even when performing timer control, and overcharge can be prevented.

Further, by providing the means described in claim 2, it is possible to accurately predict the remaining amount, and it is also useful for improving the usability. Further, as in the invention according to claim 3, by providing means for calculating the estimated charging time, the time required to charge the remaining amount of the secondary battery 23 can be obtained almost accurately, and the charging can be performed. The appropriate time for the time over can be determined.

According to the fourth aspect of the present invention, the correction value from the rated capacity to the actual capacity is obtained in the rapid charging, the remaining amount based on the actual capacity is calculated by monitoring the discharge, and the process in the standard charging is performed rapidly. By separating the processing from charging, it is possible to prevent overcharging by accurately predicting the charging time until full charging even when the charging completion cannot be detected by detecting ΔT and −ΔV in standard charging. Become.

Further, as in the fifth aspect of the invention, the correct remaining amount can be managed by correcting the remaining amount corresponding to the leak current even in the standby state.

[0025]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a block diagram of an embodiment of the present invention.

In FIG. 2 (A), the same reference numerals as those in FIG. 1 correspond to those shown in FIG. 1, and 30 is a DC − for making the electricity supplied from an external power source or a battery a stable constant voltage.
It is a DC converter. Reference numeral 31 is an operational amplifier for setting the battery voltage to an appropriate voltage when A / D conversion is applied.
Reference numeral 32 is a sense resistor for setting the current as a voltage in order to measure the current flowing out from the battery. 33 is a sense resistor 3
It is an operational amplifier for setting the voltage at both ends of 2 to an appropriate voltage when A / D conversion is applied. Reference numeral 34 is a thermistor 35 for measuring the battery temperature and a resistance for generating a voltage by resistance division. Reference numeral 35 is a thermistor.

The charging control microcomputer 15 is, for example, as shown in FIG.
It is composed of a 4-bit single-chip microcomputer as shown in FIG. It has ports (PORT0 to n) 40 for input / output and an A / D converter 41 for converting an analog voltage into a digital value. These are coupled to the internal bus 42. Further, it has a RAM 43 used as a data memory and a ROM 45 in which a micro program and the like are stored. The LCD control / drive circuit 44
It is a circuit that controls the display of the liquid crystal display for displaying the battery status. The decoding / control circuit 46 is a ROM 4
5 is a processor that performs charge control according to a microprogram stored in the memory 5.

The charging control microcomputer 15 has means for receiving inputs such as battery voltage, current and temperature, and detecting −ΔV, ΔT, etc. using the numerical values obtained by A / D conversion. Has a monitoring mechanism.

Based on these pieces of information, it is determined whether or not electricity is supplied from the charging circuit 12 to the battery, and control signals for starting and ending charging are sent to the charging circuit 12. Also,
It can have data such as charging time, and the current actual capacity of the battery is calculated by calculation from the rated capacity of the internal battery and the data of charging current. Further, from the data of the actual capacity of the battery, the maximum charging time for charging is determined, and in order to prevent overcharging, when the maximum charging time elapses, the charging circuit 12 unconditionally supplies power to the battery. Control to stop.

Since the DC-DC converter 30 and the charging circuit 12 can be constructed by known circuits, detailed description of the inside thereof will be omitted. The processing configuration of the program executed by the charging control microcomputer 15 is as shown in FIGS.

FIG. 3 shows the processing flow of the main routine relating to charging control. In the main routine, processing for changing control depending on the state of the main body of the portable computer or the like is performed. Each task ends due to a state change, returns to this main routine, and shifts to a task that performs another control. (A) to (g) in the following description correspond to the processes (a) to (g) shown in FIG.

(A) Check whether or not the AC adapter (external power supply 11) is connected. If connected, process
Proceed to (e). (b) If the AC adapter is not connected, then it is checked whether or not the portable computer or the like (the secondary battery using device 24) is operating. If it is operating, proceed to process (d).

(C) Standby (STND
BY) Start the monitoring task. (d) If it is running, start the monitoring task. (e) When the AC adapter is connected, it is checked whether or not the secondary battery using device 24 is in operation. If it is in operation, the process proceeds to step (g).

(F) If not in operation, the quick charge task is started. (g) If the secondary battery using device 24 is operating, the standard charging task is started. FIG. 4 shows a processing flow of the quick charge task. The quick charge task performs charge control during quick charge. Since the main body of a portable computer or the like can be rapidly charged only in the standby state, this routine runs when there is supply from the A / C adapter and the main body is in the standby state.

At the time of rapid charging, four controls of -ΔV, ΔT, temperature and time are performed to prevent the battery from being overcharged by any one of them. When the A / C adapter is pulled out, or when the quick charging is completed without completing the charging, the remaining amount is updated based on the charging time. This update of the remaining amount is the same for standard charging.

When the charging is completed by the control of -ΔV, ΔT, and temperature, the charging time (actual measurement time) and the charging timer value (the estimated time required for charging, which is calculated from the remaining amount at the start of charging) Is used to calculate the correction value.

The specific processing contents of the quick charge task are as shown in (a) to (s) of FIG. (a) Determine the charging conditions. The charging conditions include, for example, that the secondary battery 23 is not in a fully charged state and that the secondary battery voltage is not higher than the standard voltage.

(B) If the result of the determination of the charging condition is that charging is possible, the process (c) and the subsequent steps are executed. If charging is not possible, the processing of the quick charge task ends. In this case, if necessary, the trickle (trickle) charging phase may be entered.

(C) The charge timer value, which is the estimated time until full charge, is calculated by the following equation. Charging timer value = Rated charging time x (1-remaining amount) The rated charging time is a value obtained by dividing the rated battery capacity (mAh) by the charging current (mA), and the charging time corresponding to the remaining battery amount is calculated from this value. By subtracting, the estimated time until full charge can be obtained.

(D) Start time counting for measuring the charging time. This time counting process is a process for counting up a numerical value on a predetermined memory area by a timer processing routine (not shown) for each timer interrupt generated every 500 ms, for example. By this,
The elapsed time from the start of charging can be calculated.

(E) The value obtained by A / D converting the battery voltage is fetched. (f) Import the A / D converted value of the battery temperature. (g) Judge −ΔV. That is, check if the battery voltage from the previous sampling has dropped below a predetermined value.

(H) If it is detected by -ΔV detection that the battery is in the fully charged state, the process proceeds to the process (p). (i) Check to see if the battery temperature has reached 45 ° C or higher. When the temperature exceeds 45 ° C, it is determined that the battery is fully charged, and the process moves to (p).

(J) Determine ΔT. That is, it is checked whether the change in battery temperature from the previous sampling exceeds a predetermined value. (k) If it is detected by ΔT detection that the battery is in a fully charged state, the process moves to the process (p).

(L) The time count value and the charge timer value are compared to determine whether the charge time has expired. If the charging time is over, move to process (s). (m) Determine if the AC adapter is still connected. If the AC adapter is removed, move to process (o).

(N) It is determined whether the main body of the portable computer or the like is operating. If the operation is stopped, move to processing (o). If the main body is operating, the process (e) and subsequent steps are repeated.

(O) In order to stop the rapid charging on the way, the remaining amount is calculated by the following equation. Remaining amount = Remaining amount + Charging time ÷ (Charging timer value × Correction value) The charging time in this equation is the charging time measured by time counting, and the charging timer value is the charging timer value obtained in process (c). is there. The correction value of the charge timer value is the correction value obtained in the process (p) described later. When the remaining amount in the remaining amount storage means 20 is updated according to the calculated result, the process of the quick charging task is ended.

(P) When the battery is in a fully charged state, the actual capacity correction value is calculated by dividing the charging time measured up to that time by the time count by the charging timer value which is the predicted time.

(Q) The actual capacity of the secondary battery 23 is calculated by multiplying the rated capacity by the correction value. (r) Assuming that the remaining amount stored in the remaining amount storage means 20 is 100%,
The processing of the quick charge task ends.

(S) If the charging time is over,
The remaining amount stored in the remaining amount storage means 20 is set to 100%, and the process of the quick charging task is ended. FIG. 5 shows a processing flow of the standard charging task. The standard charging task controls charging during standard charging. When the main body of a portable computer or the like is operating, it is possible to perform only standard charging due to the ability of the A / C adapter.
There is a supply from the / C adapter, and this routine runs only when the main unit is operating.

In standard charging, since changes in −ΔV, ΔT, etc. do not significantly appear, only control by time and battery temperature is performed. When standard charging is completed without completing charging, such as when the A / C adapter is removed, the remaining amount is updated based on the charging time.

The flow of processing by the standard charging task is shown in FIG.
Processes (a) to (k) are shown in. (a) Determine the charging conditions. The charging conditions include, for example, that the secondary battery 23 is not in a fully charged state and that the secondary battery voltage is not higher than the standard voltage.

(B) If the result of the determination of the charging condition is that charging is possible, the processing (c) and the subsequent steps are executed. If charging is not possible, the standard charging task processing ends. Note that trickle charging may be performed if necessary.

(C) The charge timer value, which is the estimated time until full charge, is calculated by the following equation. Charging timer value = Rated charging time x (1-remaining amount) The rated charging time is a value obtained by dividing the rated battery capacity (mAh) by the charging current (mA), and the charging time corresponding to the remaining battery amount is calculated from this value. By subtracting, the estimated time until full charge can be obtained.

(D) The time counting for measuring the charging time is started. This time counting process is a process for counting up a numerical value on a predetermined memory area by a timer processing routine (not shown) for each timer interrupt generated every 500 ms, for example. By this,
The elapsed time from the start of charging can be calculated.

(E) A value obtained by A / D converting the battery temperature is fetched. (f) Check to see if the battery temperature exceeds 45 ° C. When the temperature exceeds 45 ° C, it is determined that the battery is fully charged, and the process (k) is performed.

(G) The time count value and the charge timer value are compared to determine whether the charge time has expired. If the charging time is over, move to process (k). (h) Determine whether the AC adapter is still connected. If the AC adapter is removed, move to process (j).

(I) It is determined whether the main body of the portable computer or the like is in operation. If the operation has stopped, move to process (j). If the main body is operating, the process (e) and subsequent steps are repeated.

(J) Since standard charging is stopped halfway, the remaining amount is calculated by the following equation. Remaining amount = Remaining amount + Charging time ÷ (Charging timer value × Correction value) The charging time in this equation is the charging time measured by time counting, and the charging timer value is the charging timer value obtained in process (c). is there. The correction value of the charge timer value is the correction value obtained in the process (p) shown in FIG. When the remaining amount of the remaining amount storage means 20 is updated according to the calculated result, the process of the standard charging task is ended.

(K) If it is determined that the battery is fully charged, the remaining amount stored in the remaining amount storage means 20 is set to 100%,
End the standard charging task process. FIG. 6A shows a processing flow of the standby monitoring task.

The standby monitoring task performs a process for calculating the power consumption of the battery in the standby state of the main body of the portable computer or the like. Measure the leak current in advance,
Thereby, the coefficient corresponding to the power consumption per unit time is determined. Then, measure the standby time,
Calculate the power consumption for that time.

That is, the standby monitoring task performs the following processes (a) to (c). (a) Start time counting. (b) Wait for status change such as operation of the main body or connection of AC adapter.

(C) If there is a state change, the coefficient determined in advance by measuring the leak current or the like multiplied by the standby time is used as the consumption amount, and this amount is subtracted from the remaining amount to correct the remaining amount. Then, the processing of the standby monitoring task ends.

FIG. 6B shows the processing flow of the monitoring task. The monitoring task executes the process of calculating the remaining battery level from the current consumption while the main unit is operating. The power consumption is calculated by measuring the current consumption for each certain sampling time (for example, 1 second to 10 seconds) and integrating it. 20% remaining
When it becomes the following, the main battery side is notified of the low battery, and when the remaining amount is 10% or less, the dead battery is notified.

The process flow of the monitoring task will be described according to the processes (a) to (h) shown in FIG. 6 (B). (a) Take in the A / D conversion result of the discharge current amount.

(B) Also, the A / D conversion result of the battery voltage is fetched. (c) Calculate the discharge amount by the following formula. Discharge amount = (discharge current x sampling time) / rated capacity Then, subtract this discharge amount from the current remaining amount to obtain the new remaining amount.

(D) to (h) The system, such as a portable computer, is notified of a low battery, a dead battery, or the like, if necessary, according to the new remaining amount. FIG. 7 shows an example of the remaining amount display on the battery status indicator 22 shown in FIG.

The battery status indicator 22 has four display blocks for displaying the remaining amount, and when the remaining amount is 0 to 10%, these blink for 10 seconds. 11-20%, 21-
The display as shown in FIG. 7 is performed in the respective ranges of 50%, 51 to 90%, 91 to 99%, and 100%.

FIG. 8 shows a usage example of the charging control device according to the embodiment of the present invention. The charging control device 10 shown in FIG. 8 is used as an auxiliary battery of the portable computer 80. This auxiliary battery is a portable computer 8
Detachable on the back of 0. An indicator 81 for displaying the remaining amount is provided on the upper surface of the auxiliary battery. Of course, the charging control device 10 according to the present invention
Can be used not only for auxiliary batteries, but also for charging control of batteries built into the main unit.

[0069]

As described above, according to the present invention,
When a device using a secondary battery is charged, overcharging can be prevented, the battery can be prevented from being destroyed, and the life of the battery can be extended. Even when predicting the remaining capacity at the time of discharging, it is possible to flexibly respond to changes in the actual capacity such as the memory effect and the deterioration of the battery, so that it is possible to accurately predict the remaining capacity. As a result, the user can systematically use the secondary battery.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a configuration diagram of an embodiment of the present invention.

FIG. 3 is a diagram showing a main processing flow according to the embodiment of the present invention.

FIG. 4 is a diagram showing a processing flow of a quick charge task according to an embodiment of the present invention.

FIG. 5 is a diagram showing a processing flow of a standard charging task according to the embodiment of the present invention.

FIG. 6 is a diagram showing a processing flow of a standby monitoring task and a monitoring task according to the embodiment of the present invention.

FIG. 7 is a diagram showing an example of remaining amount display according to an embodiment of the present invention.

FIG. 8 is a diagram showing a usage example of the charging control device according to the embodiment of the present invention.

[Explanation of symbols]

 10 Charging Control Device 11 External Power Supply 12 Charging Circuit 13 Voltage Detection Unit 14 Battery Temperature Detection Unit 15 Charging Control Microcomputer 16 Charging Time Measurement Means 17 Prediction Time Calculation Means 18 Real Capacity Calculation Means 19 Remaining Capacity Means 20 Remaining Capacity Means 21 Remaining Quantity display means 22 Battery status indicator 23 Secondary battery 24 Secondary battery using device

Claims (6)

[Claims] 1. A charging control device for controlling charging of a secondary battery (23), means for detecting completion of charging by temperature change or voltage change of the secondary battery during charging.
4,15), charging time measuring means (16) for measuring the charging time from the start to completion of charging, and a predicted time calculation for predicting the charging time until full charge based on the rated capacity and the charging current. An actual battery capacity calculating means (18) for calculating an actual battery capacity from the means (17), the measured time obtained by the charging time measuring means (16), and the estimated time obtained by the estimated time calculating means (17). ) And a charging control device. 2. The charging control device according to claim 1,
The remaining amount storage means (20) for storing the remaining amount of the secondary battery (23) based on the predicted actual battery capacity, and the remaining amount based on the charge amount and the discharge amount at the time of charging and discharging. Remaining amount calculation means (19) for updating the remaining amount stored in the storage means (20)
And a remaining amount display unit (21) for displaying the remaining amount stored in the remaining amount storage unit (20). 3. The charge control device according to claim 2,
The estimated time calculation means (17) calculates a value obtained by subtracting the charging time for the remaining amount stored in the remaining amount storage means (20) from the rated charging time as the estimated charging time, and the estimated time is calculated as the estimated charging time. A charging control device characterized by being used for stop control. 4. A charging control device for controlling charging of a secondary battery (23), wherein an external power source (11) is connected and a device (24) using the secondary battery (23) is operating. When not
Rapid charging of the secondary battery (23) is performed, a correction value of the actual capacity with respect to the rated capacity is calculated based on the actual charging time, and the actual value of the secondary battery (23) is calculated based on the correction value. Charge processing means for calculating static remaining amount and external power supply (11)
Is connected and the device (24) using the secondary battery (23) is operating, the secondary battery (23) is standardly charged, and the secondary battery is charged based on the correction value. The actual remaining amount of the battery (23) is calculated, and the charging time until full charge is predicted from the rated charging time and the remaining amount of the secondary battery (23), and the charging time is reached. When the device (24) using the secondary battery (23) is operating in a state in which the external power source (11) is not connected to the standard charge processing means that sometimes stops charging,
A charge control device comprising: a monitoring processing unit that updates the remaining amount of the secondary battery (23) based on the discharge amount. 5. The charging control device according to claim 4,
The external battery (11) is not connected and the secondary battery (23)
A standby monitoring processing means for updating the remaining amount by subtracting the leak current equivalent to the standby time from the remaining amount of the secondary battery (23) when the device (24) using A charging control device characterized by. 6. A method of controlling the charging of a secondary battery (23), the process of calculating a predicted time required to fully charge the battery when the capacity of the secondary battery (23) to be charged is a rated capacity. And a process of actually measuring the time required to fully charge the secondary battery (23) when detecting the completion of charging due to a temperature change or a voltage change, and a ratio of the actually measured time and the predicted time for charging. And a step of calculating a correction value for the rated capacity and calculating a substantial battery capacity.