JPH11187586A - Method and system for charging secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the charging capacity of a secondary battery while shortening the charging time without relying upon intricate circuitry. SOLUTION: A battery cell voltage detecting circuit 5 in a battery pack 19 compares the voltage of a battery cell 8 with the voltage of a high accuracy reference power supply 4 and delivers the voltage through battery cell voltage detecting terminals 131 , 132 to the constant voltage charging circuit 1 in a charger. The charger 15 performs constant current constant voltage charging control of a battery pack 16 using the battery cell voltage obtained through the detecting terminals 131 , 132 as a feedback signal. Since effect of the impedance of overcharge protective circuits 5, 6 built in the battery pack can be eliminated, charging time is shortened and charging capacity is enhanced. Furthermore, the circuitry is simplified because the charger requires no charging voltage detecting circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and a system for charging a secondary battery.

[0002]

2. Description of the Related Art Non-aqueous secondary batteries such as lithium ion batteries are charged at a constant current and a constant voltage. In this charging method, when charging a sufficiently charged secondary battery, constant current charging is performed at a certain set current in the initial stage of charging, and when the secondary battery voltage reaches a certain set value, constant voltage charging is performed at the set value voltage. And charge until fully charged.

FIG. 7 shows a block diagram of a conventional charging system using a charger and a battery pack in this charging method.
The battery pack 22 includes a battery cell 8, a battery cell voltage detection circuit 5 including the high-precision reference power supply 4, an overcharge detection circuit 6, and an overcharge protection switch 7. Also, includes a charging voltage detection circuit 3 including a high precision reference power supply 4 _1, a constant voltage charging circuit 1 and the constant current charging circuit 2 to the charger 11.

[0004] Non-aqueous secondary batteries such as lithium ion batteries that perform constant voltage / constant current charging are significantly deteriorated in performance due to overcharging, and are accompanied by dangers such as rupture. Therefore, battery packs using these secondary batteries are required. Has a built-in overcharge protection circuit.
The overcharge protection circuit indicates a circuit configured by the battery cell voltage detection circuit 5, the overcharge detection circuit 6, and the overcharge protection switch 7.

First, the operation of the overcharge protection circuit will be described. The battery cell voltage detection circuit 5 monitors the battery cell voltage, compares it with the voltage value of the reference power supply 4 set to a certain value, and outputs the comparison value. This output is input to the overcharge detection circuit 6 and controls ON / OFF of the protection switch 7.

The overcharge protection circuit operates to turn off the protection switch 7 when the battery cell voltage becomes higher than a preset overcharge detection voltage due to overcharge or the like.

Next, the operation at the time of charging will be described. Filling
The charging voltage detection circuit 3 built in the electric appliance 21
Terminal 9 of battery pack 22_Two Output terminal of charger connected to
Child 9 ₁ And the high voltage that determines the set voltage during constant-voltage charging.
Accuracy reference power supply 4₁ And outputs a comparison value. This
Is input to the constant voltage charging circuit 1. This charging voltage
The battery pack terminal voltage detected by the detection circuit 3 is a reference power supply.
4₁ Constant current when it is lower than the set voltage determined by
The charging circuit 2 charges the battery pack 12 at a constant current.
The charging causes the terminal voltage of the battery pack 22 to rise,
The pressure detection circuit 3 sets the terminal voltage of the battery pack 22 to the set voltage.
When it detects that it has reached
The voltage charging circuit 1 operates to charge the battery pack 22 at a constant voltage.
I do. At this time, the output signal of the charging voltage detection circuit 3 is constant.
It is a feedback signal for performing pressure charging control. I
Therefore, the charging power when the battery pack 22 is charged at a constant voltage.
The voltage value and its setting accuracy are determined by the charging voltage detection built in the charger 21.
Circuit 3 and high precision reference power supply 4 ₁ Determined by the accuracy of
You.

FIG. 8 shows a charging method for shortening the charging time.
Pulse charging method. The charging voltage at the time of constant voltage charging is set higher, and the charging operation is performed intermittently by pulse charging. According to this method, in addition to a charging circuit with a built-in charger and a protection circuit with a built-in battery pack similar to the constant current and constant voltage charging circuit of FIG. A charge switch 12 is provided.

Further, in this pulse charging system, a method of omitting a switch element built in a charger and performing a pulse charging operation with a switch element built in a battery pack for overcharge protection is described in Japanese Patent Application Laid-Open No. Hei 7-105983. Have been. In this system, the pulse charging switch 12 in FIG. 8 for pulse charging built in the charger is not required, and the system is simplified. However, the pulse control circuit 11 is still required in the charger, and the above-described constant current / current There is a disadvantage that the circuit is more complicated than the constant voltage charging method.

[0010]

When charging a battery pack containing an overcharge protection circuit and an overcharge protection switch,
When the charging current flows, the battery pack terminal voltage becomes slightly higher than the battery cell voltage due to the influence of the voltage drop of the overcharge protection circuit and the overcharge protection switch. In the constant current / constant voltage charging by the above-described systems of FIGS. 7 and 8, the charging voltage detection circuit 3 incorporated in the charger detects the terminal voltage of the battery pack as the charging voltage, and outputs the battery pack terminal voltage based on the output. , The battery cell is charged with a voltage lower than the constant voltage charge value set in the charger. FIG. 9 shows a time change of the charging voltage and the charging current at this time.

In a non-aqueous secondary battery such as a lithium ion secondary battery that performs constant current and constant voltage charging, if the charging voltage is lower than an appropriate value, the total charging capacity decreases. Conversely, charging at a voltage higher than the appropriate value may cause deterioration of the battery, possibly leading to destruction. Therefore, the charging voltage cannot be easily increased.

The influence of the impedance of the overcharge protection circuit built into the battery pack and the impedance of the overcharge protection switch 7 is shown in FIG.
At the time of constant current charging A in the initial stage of charging, the largest error occurs between the battery back terminal voltage and the electronic cell terminal voltage. Therefore, when the battery cell terminal voltage has not risen to the set voltage for constant voltage charging, the battery pack terminal voltage reaches the set voltage for constant voltage charging, and switches from constant current charging to constant voltage charging. That is, the battery cell 8 is charged at a constant voltage in a state where the terminal voltage is lower than an appropriate charging voltage and there is still room for constant current charging, and the charging current B decreases as shown in FIG. For this reason, there is an adverse effect that extra time is required until the battery is fully charged.

In the conventional constant-current / constant-voltage charging, since the charging voltage is detected and the constant voltage is controlled with respect to the battery pack terminal voltage, the capacity of the battery cell cannot be sufficiently extracted as described above. The disadvantage is that the time is lengthened. On the other hand, if a slightly higher charging voltage is set in advance for the battery pack terminal in anticipation of this error, the above-mentioned adverse effects can be improved, but it is difficult to take measures to prevent a decrease in safety and battery performance.

In the pulse charging by the charging system shown in FIG. 8, even if the charging voltage is set to be higher due to the intermittent charging operation, the charging time can be reduced without affecting the battery safety and the battery deterioration preventing performance. Shortening and improvement of charging capacity can be achieved. However, as shown in FIG. 8, since the charger for realizing this method requires a switching control circuit including a pulse control circuit and a pulse charging switch, there is a disadvantage that the configuration becomes very complicated. is there.

[0015] The object of the present invention is not to use a complicated circuit,
Improve charging capacity and shorten charging time.
An object of the present invention is to provide a secondary battery charging method and system.

[0016]

According to the present invention, there is provided a method of charging a secondary battery, the method comprising: charging a battery cell of a secondary battery pack with a charger; Detecting a voltage; and controlling charging of the battery cell by the charger in accordance with the voltage of the battery cell detected in the step.

The step of detecting the voltage of the battery cell includes the step of transmitting the detected voltage of the battery cell, and the step of controlling charging of the battery cell includes the step of controlling the voltage of the transmitted battery cell. It may receive at a connection terminal and control charging of the battery cell according to the battery cell voltage.

The step of detecting the voltage of the battery cell of the secondary battery pack includes the step of generating a reference voltage of the battery cell voltage and the step of measuring the voltage of the battery cell and comparing the measured voltage with the reference voltage of the battery cell voltage. And sending the comparison result to the charger, and controlling the charging of the battery cell by the charger includes receiving the comparison result at the connection terminal, and obtaining the comparison result through the connection terminal. Detecting the battery cell voltage based on the comparison result obtained and switching the charging of the battery cell from constant current charging to constant voltage charging using the battery cell voltage as a feedback signal.

The secondary battery charging system according to the present invention is a secondary battery charging system comprising: a secondary battery pack having secondary battery cells; and a charger for charging the secondary battery cells. The battery pack has a battery cell voltage detection circuit for detecting a voltage of the secondary battery cell, and the charger controls charging of the battery cell according to a detection result of the battery cell voltage detection circuit.

The charger has a connection terminal for receiving the voltage value of the battery cell to be charged from the secondary battery pack, and uses the battery cell voltage obtained through the connection terminal as a feedback signal to set the battery cell constant. Voltage charging may be performed.

The secondary battery pack has positive and negative terminals for charging and discharging, a high-precision reference power supply for generating a reference battery cell voltage, a voltage of the battery cell and a reference voltage generated by the high-precision reference power supply. A battery cell voltage detection circuit that compares the battery cell voltage detection circuit, a positive / negative connection terminal for sending the detected battery cell voltage to the charger as a feedback signal, and an output of the battery cell voltage detection circuit as inputs, and a set value. The circuit includes an overcharge detection circuit for comparison, and an overcharge source protection switch that shuts off a charging current when the overcharge detection circuit detects a battery cell voltage higher than a set value.

[0022]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a first method of charging a secondary battery according to the present invention.
9 is a flowchart of the embodiment.

As shown in FIG. 1, in the method of charging a secondary battery according to the first embodiment, first, a voltage of a battery cell of a secondary battery pack is detected (step 1). Next, the detected battery cell voltage is transmitted to the charger (step 2). Subsequently, the transmitted battery cell voltage is received at the connection terminal of the charger (step 3). Subsequently, charging of the battery cell of the secondary battery is controlled according to the electronic cell voltage received by the charger (step 4).

In the charging method of this embodiment, the charging capacity of the secondary battery is improved by a relatively simple charging system.
In addition, the charging time can be reduced.

FIG. 2 shows a second method of charging a secondary battery according to the present invention.
9 is a flowchart of the embodiment.

The charging method of the secondary battery of the second embodiment is shown in FIG.
First, a reference voltage of the battery cell of the secondary battery pack is generated by a high-precision reference power supply (step 1).
1). Next, the voltage of the battery cell is compared with the voltage generated by the high-precision reference power supply (step 12), and the comparison value is sent to the charger (step 13). Subsequently, the comparison value is received at the connection terminal of the charger (step 14). Subsequently, the charger detects the battery cell voltage from the comparison value (step 15).
Subsequently, constant voltage charging of the battery cell is performed using the detected battery cell voltage as feedback (step 16).

In the charging method of this embodiment, the charging capacity of the secondary battery is improved by a relatively simple charging system.
In addition, the charging time can be reduced.

FIG. 3 is a block diagram of a first embodiment of a secondary battery charging system to which the charging method of FIG. 2 is applied, and FIG. 4 is a detailed view of the secondary battery charging system of FIG. FIG. 5 is a graph showing charging characteristics of the secondary battery charging system of FIG.

The secondary battery charging system of this embodiment is
As shown in FIG. 3, the charger 15 and the battery pack 16
The charger 15 is a charger of the secondary battery charging system of FIG.
21 high-precision reference power supplies 4₁ Voltage detection circuit 3 including
Instead of battery cell voltage detection terminal (+) 13₁ And battery cells
Voltage detection terminal (-) 14₁ Is provided, and the battery pack 16
Is a battery cell voltage detection terminal (+) on the battery pack 22 of FIG.
13_Two And battery cell voltage detection terminal (-) 14_Two Provided
Battery cell voltage detection terminal (+) 13_Two Has a battery cell
One of the outputs of the pressure detection circuit 5 is connected, and the battery cell voltage detection is performed.
Output terminal (-) 14 _Two Is connected to one pole of the battery cell 8
You.

The charger 15 and the battery pack 16 are connected by charging terminals (+) 9 ₁ and 9 ₂ and charging terminals (−) 10 ₁ and 10 ₂ , and a battery cell voltage detecting terminal (+) 13
₁ , 13 ₂ and battery cell voltage detection terminals (−) 14 ₁ , 14
Connected by _two .

The constant voltage charging circuit 1 built in the charger 15 is a constant current / constant voltage supply circuit.
3 _1, 13 _2, 14 _1, 14 ₂ through the battery pack 16
The constant voltage charging is performed using the output of the battery cell voltage detection circuit 5 built in the battery pack sent from the control unit as a feedback signal. Therefore, accurate constant voltage charging control can be performed on the battery cells 8. Further, since the function of sharing the battery cell voltage detection circuit 5 including the high-precision reference power supply 4 as the overcharge protection circuit and the charging voltage detection circuit is achieved, the circuit of the charger can be simplified.

Next, details will be described with reference to FIG.

First, a protection circuit built in the battery pack 16 includes a battery cell voltage detection circuit 5, an overcharge detection circuit 6,
It comprises an overcharge protection switch 7 and positive and negative battery cell voltage detection terminals.

The battery cell voltage detection circuit 5 uses a battery cell voltage value obtained by dividing the battery cell voltage by the battery cell voltage detection resistors RB1 and RB2, and a voltage value of the high-precision reference power supply 4 by the charging voltage detection resistors RB3 and RB4. It has an error amplifier 18 for comparing the reference voltage value by resistance-dividing, its output is input to the constant voltage charging circuit 1 of the battery cell voltage detection terminal (+) 13 _2, 13 ₁ through the charger 17. Also,
The gain of the error amplifier 18 is determined by the gain setting resistor RB7. Battery cell voltage detection resistors RB1 and RB2, high-precision reference power supply 4, and charging voltage detection resistors RB3 and RB4
Near the appropriate charging voltage of the battery cell 8.
Is set to work.

The overcharge detection circuit 6 includes resistors RB1 and RB2.
The comparator 19 compares the battery cell voltage value divided by the resistance with the reference voltage value obtained by dividing the voltage value of the high-precision reference power supply 4 by the overcharge detection resistors RB5 and RB6. Connected to the gate of protection switch 7. The battery cell voltage detection resistors RB1 and RB2, the high precision reference power supply 4, and the overcharge detection resistors RB5 and RB6 are:
When the battery cell voltage reaches the overcharge voltage, the comparator 19 is operated and the overcharge protection switch 7 is turned off.

Next, the charger 15 will be described. The charger 15 includes a constant voltage charging circuit 1, a constant current charging circuit 2, positive and negative charging terminals 9 ₁ and 10 _1, and battery cell detection terminals 13 ₁ and 13.
Consists of _two .

The constant current charging circuit 2 has an NPN type constant current control transistor QC1, and a constant current / constant voltage control resistor RC1 is connected between its base and emitter. Here, the constant current value of the constant current charging circuit 2 is the transistor Q
It is determined by the base-emitter voltage of C1 and the resistance of resistor RC1.

The constant voltage charging circuit 1 is an NPN type constant current
It has a constant voltage control transistor QC2 and an NPN-type constant voltage control transistor QC3 for driving its base. A constant voltage / constant current control transistor driving resistor RC is provided between the collector and base of the constant voltage / constant current control transistor QC2.
2 has a constant voltage control resistor RC3 connected to the emitter of the constant voltage control transistor QC3. The base of the constant voltage control transistor QC3 is a battery cell voltage detection terminal (+) 1
3 battery cell voltage detection circuit 5 in ₁ through the battery pack 16
The battery cell voltage is driven by the output of
6 is driven so as to be kept constant at the charging voltage set by the battery cell voltage detecting circuit 5.

Next, a charging operation by this charging system will be described. FIG. 5 shows the charging voltage and the charging current with respect to the charging time. At the beginning of charging, while the battery cell voltage is low, the battery cell voltage detection circuit 5 in the battery pack 16
The output of the (error amplifier 18) is low, the constant voltage charging circuit 1 of the charger 15 does not operate, and the constant current charging circuit 2 performs constant current charging (C in FIG. 5). When charging proceeds and the battery cell voltage reaches a preset charging voltage, the output of the battery cell voltage detection circuit 5 of the battery pack 16 causes the transistors QC3 and QC of the constant voltage charging circuit 1 of the charger 15 to output.
2 is driven to perform constant voltage charging (D in FIG. 5).

At this time, the charging in which the battery cell voltage is set
When the voltage rises, the error of the battery cell voltage detection circuit 5 is canceled.
The output of the pump 18 rises and the battery cell voltage detection terminal 13₁ ,
13 _Two The signal transmitted through the charger 15
Voltage of the transistor QC3 of the constant voltage charging circuit 1 of FIG.
Rise, and the collector current increases due to the resistor RC3. So
As a result, the voltage drop due to the resistor RC2 increases,
Direction to lower the base voltage of the star QC2 and lower the charging voltage
Works. Conversely, the battery cell voltage is lower than the set voltage.
When the voltage drops, the reverse operation is performed to increase the charging voltage.
You.

When the charging voltage becomes higher than the overcharging voltage set by the overcharge detecting circuit 6 of the battery pack 19 due to some problem such as a failure of the charger 15 during charging, the output of the comparator 19 becomes low, and the battery becomes low. The overcharge protection switch 7 of the pack 16 is turned off, and the charging is forcibly stopped by cutting off the charging path.

The charging voltage is kept constant by this series of feedback systems. The charging current at the time of low voltage charging is determined by the state of charge of the battery. When the charging current gradually decreases and becomes full, the charging current stops flowing and the charging is completed.

FIG. 6 is a detailed block diagram of a second embodiment of a secondary battery charging system to which the secondary battery charging method of FIG. 2 is applied.

In this secondary battery charging system, a charger 17 is used instead of the charger 5 shown in FIG. In the charger 17, the constant current charging circuit 1 and the constant voltage charging circuit 2 include a variable three-terminal regulator IC1, a charging current setting resistor RC1, a constant voltage control resistor RC2, and a low voltage control transistor QC1.

The resistors RC1 and RC2 are connected between OUT-ADJ of the variable three-terminal regulator IC1, and the constant voltage control transistor QC1 is connected between ADJ of the variable three-terminal regulator IC1 and the battery cell detection terminal (-). .
The battery cell voltage detection terminal (+) 13 ₁ is connected via a resistor RC3 to the base of the transistor QC1. Charging terminal (+) 9 ₁ is connected between the resistors RC1 and RC2.

At the beginning of charging, while the battery cell voltage is close, the low voltage control transistor QC1 is off, and the voltage between OUT-ADJ of the variable three-terminal regulator IC1 and the resistance RC1
Is supplied to the battery pack 16. At this time, the charging voltage is determined by the state of the battery cell 16 and gradually increases. When charging proceeds and the battery cell voltage rises to a voltage value at which constant-voltage charging should be performed, the constant-voltage control transistor QC1 turns on, and the mode shifts from the constant-current charging mode to the constant-voltage charging mode.

At this time, when the battery cell voltage rises above the set charging voltage, the collector current flowing through the constant voltage control transistor QC1 increases, and the variable three-terminal regulator I
The potential of the ADJ terminal of C1 decreases, and the charging voltage is reduced. Conversely, when the battery cell voltage falls below the set charging voltage, the potential of the ADJ terminal rises and attempts to increase the charging voltage. By such a series of feedback operations, the charging voltage is kept constant with respect to the battery cells 8 as in the first embodiment shown in FIG.

When the constant voltage charge control does not function well due to a failure of the charger or the like and the charge voltage becomes too high, the output of the comparator 19 of the overcharge detection circuit 6 becomes low and the overcharge protection switch 7 is turned off. In addition, the charging current flow path is interrupted to forcibly stop charging.

In such a series of charging operations, the detection accuracy of the charging voltage and the setting of the charging voltage depend on the accuracy and set values of the reference power supply 4 and the battery cell voltage detecting resistor of the battery cell voltage detecting circuit 5 built in the battery pack 16. Decided. The accuracy and the set value of the charging current during the constant current charging are determined by the accuracy and the set value of the constant current control resistor RC1 of the charger 17. Non-aqueous secondary batteries typified by lithium ion batteries are vulnerable to overcharging and require high accuracy in voltage setting during constant voltage charging.
On the other hand, the charging current has a wide range that can be arbitrarily selected, and high accuracy is not required.

[0051]

As described above, the present invention uses the output of the battery cell voltage detecting circuit built in the battery pack as a feedback signal to the charger for constant voltage charging of the charger, thereby controlling the charging voltage. Works on the battery cell voltage, not on the terminal voltage of the battery pack, so there is no charge voltage error due to the influence of the impedance of the protection circuit and protection switch. This has the effect of shortening the charging time while maintaining safety against overcharging. Also, since the battery cells are charged with an appropriate voltage value,
The charging capacity can be increased, and a charging voltage detection circuit including a high-precision reference power supply and a charging voltage detection resistor for constant voltage charging control of the charger is not required, so that the charging circuit of the charger can be simplified. This has the effect.

[Brief description of the drawings]

FIG. 1 is a flowchart of a first embodiment of a method for charging a secondary battery according to the present invention.

FIG. 2 is a flowchart of a second embodiment of the method for charging a secondary battery according to the present invention.

FIG. 3 is a block diagram of a first embodiment of a secondary battery charging system of the present invention to which the charging method of FIG. 2 is applied.

FIG. 4 is a detailed view of the secondary battery charging system of FIG.

FIG. 5 is a graph showing charging characteristics of the secondary battery charging system of FIG.

FIG. 6 is a detailed block diagram of a second embodiment of the secondary battery charging system of the present invention to which the charging method of FIG. 2 is applied.

FIG. 7 is a block diagram of a first conventional example of a secondary battery charging system.

FIG. 8 is a block diagram of a second conventional example of a secondary battery charging system.

FIG. 9 is a graph showing charging characteristics of the secondary battery charging system of FIG.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 constant voltage charging circuit 2 constant current charging circuit 4 high precision reference power supply (built-in battery pack) 5 battery cell voltage detection circuit 6 overcharge detection circuit 7 overcharge protection switch 8 battery cell 9 ₁ , 9 ₂ charging terminal (+) 10 ₁ , 10 ₂ Charging terminal (−) 13 ₁ , 13 ₂ Battery cell voltage detecting terminal (+) 14 ₁ , 14 ₂ Battery cell voltage detecting terminal (−) 15, 17 Charger 16 Battery pack 18 Error amplifier 19 Comparator RB1, RB2, RB3, RB4, RB5, RB6, R
B7 Resistance RC1, RC2, RC3 Resistance QC1, QC2, QC3 Transistor IC1 Variable three-terminal regulator C Constant current charging D Constant voltage charging

Claims (6)

[Claims] 1. A method for charging a secondary battery in which a battery cell of a secondary battery pack is charged by a charger, comprising: detecting a voltage of a battery cell of the secondary battery pack; and detecting the battery detected by the step. Controlling the charging of the battery cell by the charger according to the voltage of the cell. 2. The step of detecting the voltage of the battery cell,
Transmitting the detected voltage of the battery cell, controlling the charging of the battery cell, receiving the transmitted voltage of the battery cell at a connection terminal, and setting the battery according to the battery cell voltage. The method for charging a secondary battery according to claim 1, wherein charging of the cell is controlled. Detecting a voltage of a battery cell of the secondary battery pack; generating a reference voltage of the battery cell voltage; measuring a voltage of the battery cell and comparing the measured voltage with the reference voltage of the battery cell voltage. And transmitting the comparison result to the charger; controlling charging of the battery cell by the charger; receiving the comparison result at the connection terminal; and the connection terminal Detecting the battery cell voltage based on the comparison result obtained through the above, and performing charging of the battery cell by switching from constant current charging to constant voltage charging using the battery cell voltage as a feedback signal. 2. The method for charging a secondary battery according to claim 1. 4. A secondary battery charging system, comprising: a secondary battery pack having secondary battery cells; and a charger for charging the secondary battery cells, wherein the secondary battery pack comprises the secondary battery cells. A secondary battery charging system, comprising: a battery cell voltage detection circuit that detects a voltage of the battery cell; and the charger controls charging of the battery cell according to a detection result of the battery cell voltage detection circuit. 5. The battery charger has a connection terminal for receiving a voltage value of a battery cell to be charged from the secondary battery pack, and uses the battery cell voltage obtained through the connection terminal as a feedback signal as the feedback signal. 5. The secondary battery charging system according to claim 4, wherein the charging of the secondary battery is switched from constant current charging to constant voltage charging. 6. The secondary battery pack includes: a positive / negative terminal for charging and discharging; a high-precision reference power supply for generating a reference battery cell voltage; a battery cell voltage and the high-precision reference power supply; A battery cell voltage detection circuit that compares the reference voltage with the battery cell voltage detection circuit, a positive / negative connection terminal for sending the detected battery cell voltage to the charger as a feedback signal, and an output of the battery cell voltage detection circuit as an input, 6. The secondary battery according to claim 5, further comprising: an overcharge detection circuit that compares the set value with an overcharge detection circuit; and an overcharge source protection switch that shuts off a charging current when the overcharge detection circuit detects a battery cell voltage higher than the set value. Charging system.