JPH1189109A - Charging control method of secondary battery and charger thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging control method of secondary battery and a charger thereof, which can discriminate the full-charging condition of a secondary battery using a simple structure, without directly detecting charging current. SOLUTION: A voltage value obtained by adding the battery voltage of a battery 14 and the voltage by a current setting resistor R1 series-connected to a charging line is detected through a voltage detection input (A/D) of a controller 22 while a control FET18 is being charged in an on condition, and it is discriminated as to whether the battery 14 is charged fully based on a change in the voltage value, for example, a voltage change which changes by a very small amount downward from the maximum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging control method for a secondary battery for charging a secondary battery and a charging apparatus for the same.
For example, the present invention relates to a charge control method for a secondary battery that charges a secondary battery such as a lithium ion battery, a nickel cadmium battery, and a nickel hydride battery, and a charging device thereof.

[0002]

2. Description of the Related Art In recent years, electronic devices such as mobile phones, notebook computers, and digital cameras have become smaller and lighter. With the spread of electronic devices, they can be repeatedly charged and discharged as a power source for driving the electronic devices. Opportunities for use of secondary batteries are increasing. As such a secondary battery, for example, a nickel cadmium (Ni-Cd) battery, a nickel hydrogen (Ni-MH) battery, a lithium ion battery and the like are known. For example, lithium ion secondary batteries
Unlike other secondary batteries that generate electricity by an electrochemical reaction involving water using an aqueous electrolyte, for example, a non-aqueous secondary battery using an organic solvent of a lithium salt for the electrolyte, lithium ion It is configured to generate electricity by an oxidation-reduction reaction caused by the movement of the hydrogen. Such a non-aqueous secondary battery has the advantage that the voltage between battery terminals in a single cell is high, and has high capacity and high output, as compared with other secondary batteries. A charging method for improving the performance of the battery itself and for more effectively using the non-aqueous secondary battery is being studied.

For example, conventionally, a charging current measuring resistor for detecting a charging current with high accuracy is inserted in series on a positive side of a charging line for charging a secondary battery, and a voltage generated at both ends of the current measuring resistor is inserted. Is amplified by an amplifier, the current charging current is estimated from the amplified value, and whether the lithium ion secondary battery is fully charged is determined by comparing the estimated charging current with the current value for determining full charge. Was.

[0004]

However, in the conventional charging apparatus, since the magnitude of the charging current is detected to determine whether or not the battery is fully charged, a high-precision charging current measuring resistor for detecting the charging current is required. Was needed. The charging current measuring resistor is required to have a resistance value of, for example, 0.1 ohm and an accuracy of ± 0.5%. Also, in order to recognize this current value with high accuracy, a high-precision amplifier or the like for amplifying the charging current value is required, which causes an increase in the actual area of parts and further reduction in the size of the charging device. It was difficult. Further, since a highly accurate circuit for detecting the charging current is required, the cost is increased, and it is difficult to construct a charging device with a simple configuration.

[0005] The present invention solves the above-mentioned drawbacks of the prior art, and accurately detects the full charge of the secondary battery with a simple configuration.
An object of the present invention is to provide a charge control method for a secondary battery and a charge device thereof, which can perform charge control reliably.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a method for controlling the charging of a secondary battery for charging a secondary battery, the method comprising the steps of: Detecting a first voltage obtained by adding a voltage of a current setting resistor that is connected in series to the battery and connected to a circuit ground and that sets a current value for the secondary battery;
A change in the first voltage during charging for charging the secondary battery is detected, and it is determined whether or not the secondary battery is fully charged based on the detected voltage change. The charging of the secondary battery is controlled.

In this case, it is preferable to detect a voltage change in which the first voltage drops from the maximum value by comparing with a predetermined value for judging whether the secondary battery is fully charged.

Further, a second voltage obtained by adding the first voltage and a voltage of an additional resistor connected in series to a charging path for charging the secondary battery is detected, and a second voltage during charging is detected. The charging of the secondary battery may be controlled based on the voltage change.

In this case, it is preferable to detect a voltage change in which the first voltage drops from the maximum value by comparing the voltage change with a predetermined value for determining whether the secondary battery is fully charged.

[0010] The predetermined value may be selected according to the type of the secondary battery.

In the charging process for the secondary battery, the secondary battery may be charged by a constant current-constant voltage charging method, and it may be determined whether the secondary battery is fully charged during the constant voltage charging. .

Further, in this method, the type of the secondary battery is determined according to the state of a switch for identifying the type of the secondary battery, and when it is determined that the secondary battery is a lithium ion secondary battery, the voltage is determined. After detecting the change, charging may be continued for a certain period of time and then terminated.

In this case, when it is determined that the secondary battery is a secondary battery other than the lithium ion secondary battery according to the state of the switch, charging may be terminated immediately upon detecting a voltage change.

It is preferable that the fixed time is selected according to the configuration of the secondary battery.

In this method, it is preferable to detect a voltage change in which the voltage at the time of charging goes from a maximum to a decrease.

According to another aspect of the present invention, there is provided a secondary battery charging apparatus for charging a secondary battery.
The device includes a charging switch that connects and disconnects a DC power supply that charges the secondary battery to and from the secondary battery according to a control signal,
Generate a control signal to turn on / off the charge switch,
Charging means for controlling charging of the secondary battery, a current setting resistor connected in series with the secondary battery to set a current value for the secondary battery, and adding the voltage of the current setting resistor and the battery voltage of the secondary battery Control means for determining the full charge of the secondary battery, wherein the control means detects that the first voltage at the time of charging for charging the secondary battery changes, It is characterized in that charging of the secondary battery is controlled based on the detected voltage change.

In this case, the device includes an additional resistor connected in series to a charging path for charging the secondary battery, and the control means includes: a battery voltage; a voltage of a current setting resistor;
It is preferable to detect a second voltage obtained by adding the voltage of the additional resistor.

The control means may detect the voltage change by comparing it with a predetermined value for judging whether the secondary battery is fully charged.

In this case, the control means preferably selects a predetermined value according to the type of the secondary battery.

The charging means performs a charging process for charging the secondary battery by a constant current-constant voltage charging method, and the control means determines whether or not the secondary battery is fully charged at the time of constant voltage charging. Good to do.

Further, the apparatus includes a switch for identifying the type of the secondary battery, and the control means determines the type of the secondary battery according to the state of the switch, and determines whether the secondary battery is a lithium ion secondary battery. When it is determined that charging is completed, the charging may be terminated after a voltage change is detected and charging is continued for a certain period of time.

In this case, when the control means determines that the secondary battery is a secondary battery other than the lithium ion secondary battery according to the state of the switch, the control means terminates the charging immediately upon detecting a voltage change. Good.

In this case, the other secondary battery is preferably a nickel cadmium battery.

Further, the other secondary battery is preferably a nickel-metal hydride battery.

It is preferable that the control means selects a fixed time according to the configuration of the secondary battery and terminates the charging after a lapse of the selected fixed time.

The control means may detect a change in the voltage at the time of charging from a maximum to a decrease.

[0027]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a charge control method for a secondary battery according to an embodiment of the present invention;

Referring to FIG. 1, there is shown an embodiment of a charging apparatus to which the present invention is applied. This charging device 10
Receiving the DC power output supplied from the adapter 12, the battery 14 removably connected to the output terminals 100a and 100b is charged. At this time, the fully charged state of the battery 14 is reliably detected, and the charging process is completed. It is a charging device configured to perform charging control such as. In the following description, parts not directly related to the present invention are not shown and described, and reference numerals of signals are represented by reference numerals of connection lines in which the signals appear.

The AC adapter 12 inputs, for example, a 100 volt commercial AC power to the terminals 102a and 102b, rectifies and smoothes them, and outputs a DC power for charging the battery 14 between the output terminals 104a and 104b. DC power supply. This DC power supply output is connected to each circuit inside the charger 10 and has a function of driving each circuit, but the description of the configuration is omitted.

The positive terminal 104a of the charger 10 is connected to a source 106 of a control FET 18 by connecting a diode 16 for preventing current backflow in series. The terminal 104b to which the negative side of the AC adapter 12 is connected is connected to the ground of the charger 10.
(AC-GND). The charge control output (EXT) of the charging IC 20 is connected to the gate 108 of the control FET 18 and the control FET 1
Reference numeral 8 has a charge switch function of shutting off or connecting between the source 106 and the drain 120 according to the gate potential High and Low, and supplying the DC output of the AC adapter 12 to the terminal 100a. The drain 120 of the control FET 18 is charged.
The battery voltage detection input (CEL) of the IC 20 and the voltage detection input (A / D) of the controller 22 are connected to each other.

On the other hand, a terminal 100b of the charger 10 is connected to a voltage detection input (CS) of the charging IC 20, and a current setting resistor (R1) 24 for setting a current value in constant current charging is connected in series. The ground (AC-GND) of the charger 10 is connected to the charging IC 20 and the controller 22. Therefore, the charging current is AC
Diode 16, control FET 18 from adapter 12 (terminal 104a)
, Battery 24, current setting resistor (R1) 24, ground (AC-GN
The terminal 100b, which passes through the path D) and is connected to the negative side of the battery 14, is not directly connected to the ground (AC-GND).

The charging IC 20 is an integrated circuit that controls the voltage and current applied to the battery 14 by giving a control signal (EXT) for turning on and off the source and drain of the charging FET 18 to its gate. The charging IC 20 in the present embodiment has a function of detecting the terminal voltage of the battery 14 appearing between the battery voltage detection input (CEL) and the voltage detection input (CS) .For example, the battery 14 can be charged by this voltage value. It is determined whether or not the battery is in a normal state in which a proper voltage is generated, and if it is determined that the battery is defective, control is performed so that charging is not started. This terminal voltage is measured when the source-drain of the control FET 18 is turned off. The charging IC 20 has a function of detecting a voltage between the voltage detection input (CS) and the ground (GND). , And shifts from constant current charging control to constant voltage charging control. Further, the charging IC 20 has a function of stopping the charging of the battery 14 by controlling the control FET 18 to the off state when the charging control signal 122 indicating the fully charged state is input. The charge control signal 122 is supplied from the controller 22, and the controller 22 is connected to a terminal connected to the battery 14.
A control circuit that detects a voltage between 104a and ground (AC-GND) and controls charging of the battery 14 according to a change in the voltage value.

As shown in FIG. 2, when the controller 22 detects that the voltage value applied to the voltage detection input (A / D) changes from the maximum value to the decrease value in accordance with the degree of the change, the controller 22 charges the battery 14. Is determined to have switched from constant current charging to constant voltage charging, and then when the battery 14 is determined to be fully charged, a charging control signal indicating this is supplied to the input (SW1) of the charging IC 20 to stop the charging process. This is a charge control circuit for causing the battery to be charged. Note that, in the figure, the curve 200 is the voltage input (A
/ D), the curve 202 shows the change in the battery voltage, and the broken line 204 shows the change in the charging current. A dashed-dotted line 206 shows a full charge determination line based on the charge current when the full charge is determined based on the charge current in the related art.

In this embodiment, the controller 22 charges the battery according to a change in the voltage applied to the voltage detection input (A / D).
It has a function of determining the constant voltage charging state of the IC 20 and performing charging control according to the type of the battery 14, that is, the state of the status switch 30. Further, the controller 22 has a full charge processing function of judging a full charge state of the battery 14 according to the voltage value of the voltage detection input (A / D), and terminating the charging according to the result. The controller 22 has a terminal
It has a function of determining whether the battery 14 connected to the battery 100 is already fully charged. If the battery 14 is not fully charged, the control FET 18 is turned on to start charging.

The battery 14 is a battery pack including a lithium ion secondary battery in which one battery cell or a plurality of battery cells are connected in series and / or parallel and housed in a predetermined case. This battery pack has a protection circuit for protecting the battery cells from overcharge and overdischarge.
In this embodiment, a lithium ion secondary battery is described as an example.However, the present invention is not limited to this, and another secondary battery such as a nickel cadmium secondary battery or a nickel hydride battery may be employed in the battery pack. Turn on / off the status switch 30 to switch the battery type connected to 22.
The charging process control is switched according to the off state. Note that the switch 30 is not limited to a manual operation or a mechanical switch, and for example, changes the type of the secondary battery in which the battery 14 is housed, such as electric / magnetism, light, etc., which change when the battery 14 is mounted on the charger 10. The detection may be performed according to the coupling state.

FIG. 3 shows the basic structure of the secondary battery. The inside of the secondary battery has a battery E for generating a battery voltage [V1]. The charging current [i] is supplied to the secondary battery E from the positive electrode to the negative electrode side and charged. The charging voltage during charging in which the charging current is flowing, that is, the terminal 100a in FIG.
-The voltage [V] between ground (AC-GND) is the battery voltage [V1],
It is a value obtained by adding the current setting resistance voltage [i × R1]. In addition,
In this figure, the voltage relating to the battery internal resistance is omitted.

[0037]

[Equation 1] Charging voltage [V] = battery voltage [V1] + current setting resistance voltage [i × R1] Therefore, at the voltage detection input (A / D) of the controller 22, the battery voltage [V1] and the current setting Resistance voltage [i × R1] = [V
2] and the value [V] is detected.

[0038]

[V] = [V1] + [V2] Here, when the constant current charging shown in FIG. 2 progresses to a constant voltage charging state, the charging current [i] decreases and the current setting resistance voltage Voltage [V2] drops, and the charging voltage also drops. Then, when the voltage detected at the voltage detection input (A / D) drops by a minute predetermined value [k] from the maximum value, that is, when [-ΔV] is detected, the controller 22 determines the charging voltage drop. It is determined that there is [−ΔV] and the constant-current charging has been switched to the constant-voltage charging, and appropriate charging control according to the battery type of the battery 14 is performed. As shown in the figure, the voltage value detected by the controller 22 is a value obtained by adding the voltage of the resistor R1 to the terminal voltage of the battery in both the constant current charging and the constant voltage charging in this embodiment. The controller 22 that performs charge control
If the status of the status switch 30 indicates a lithium ion secondary battery and a voltage drop [-ΔV] is detected,
The remaining constant voltage charging time corresponding to the type and capacity of the battery 14 is selected and set, and the time is measured. When the set time elapses, it is determined that the battery is fully charged, and the charging is terminated. Perform charge control. When the state of the switch 30 indicates a nickel-cadmium battery or a nickel-metal hydride battery, the controller 22 outputs a voltage drop [-ΔV]
, It is determined that the secondary battery is fully charged, and charge control for immediately terminating the charge is performed.

The controller 22 receives the voltage input (A
/ D) is converted to a digital value and the changes in these voltages are stored, and the value of the change from the maximum value of the voltage [V] to the decrease becomes equal to the predetermined value [k]. When it is detected that the charging process has been completed, a full charging process for terminating the charging process immediately or after a lapse of a predetermined time according to the type of the battery 14 is performed. This value [k] is a value for determining full charge, and is set to an appropriate value according to the configuration of the battery 14 such as the type of secondary battery.

As described above, in this embodiment, the charging is controlled by the method of detecting the minute drop [-ΔV] of the charging voltage [V] including the voltage [V2] of the current setting resistor.
Alternatively, for example, a change in the voltage value near the maximum value of the charging voltage may be detected.

The operation of the charging apparatus 10 according to the present embodiment having the above configuration will be described below with reference to FIG.

The charging device 10 in this embodiment performs constant-current charging from the start of charging until the charging voltage reaches a peak, and the charging IC 20 reduces the charging current after the peak.
When the voltage is detected by the voltage detection input (CS), the charging process is performed in accordance with the control of the charging IC 20 so as to shift to the constant voltage charging and charge the battery 14. In this constant voltage charging process, a charging control signal is output from the controller 22 and the charging is performed.
The control FET 18 is turned on by the output 108 of the IC 20. When the control FET 18 is turned on, the charging current from the AC adapter 12 is sequentially supplied to the battery 14, and the constant voltage charging is continued.

In step 400, the voltage value applied to the voltage detection terminal (A / D) of the controller 22 during the constant voltage charging is detected and recognized as a digital value. In step 504, the controller 22 determines whether or not a voltage drop [-ΔV] has occurred. If the voltage drop [-ΔV] has not yet occurred, the process returns to step 400, and the process proceeds to step 400. If the occurrence is detected, the process proceeds to step 404.

Step 404 where voltage drop [-ΔV] is detected
In, the type of the battery 14 being charged connected to the terminal 100 is recognized by the connection state of the switch 30, and
If the device has a lithium ion secondary battery, the process proceeds to step 406; otherwise, the process proceeds to step 410.
And the charging process is terminated. When the process proceeds to step 406 in the case where the lithium ion secondary battery is being charged, the time for measuring the remaining constant voltage charging time during the constant voltage charging is set in the timer, and the timer is started. Then, the process proceeds to step 480, where it is determined whether or not the set time has elapsed. If the set time has not elapsed, the process returns to step 406 to continue the time measurement. When the set time has elapsed, the routine proceeds to step 410, where a charge control signal for stopping charging assuming that the battery 14 is fully charged is supplied to the charging IC 20, the control FET 18 is controlled to be in an off state, and charging is completed. Thus, the full charge of the secondary battery was determined without directly detecting the charging current, and the charging process for the battery 14 was performed reliably.

Next, another embodiment to which the present invention is applied will be described with reference to FIG. FIG. 2 shows the charging device shown in FIG.
Ten application charging devices 60 are shown.

The charging device 60 in this embodiment has a control FE
The point that an additional resistor R3 is connected in series between the drain of T18 and the terminal 100a is different from the charging device 10 shown in FIG.

FIG. 7 shows the basic principle configuration of the secondary battery in this embodiment. The inside of the secondary battery includes a battery E that generates a battery voltage [V1], and a charging voltage during charging in which a charging current [i] flows, that is, a terminal 100a-ground (A) in FIG.
The voltage [V] between C and GND is the additional resistance resistance voltage [V3] = [i × R
3], battery voltage [V1], and current setting resistance voltage [V2] = [i × R
1] is applied to the voltage detection input (A / D) of the controller 22 and detected. Therefore,
In the present embodiment, the voltage value detected by the controller 22 is
[V3], the change in the charging voltage that changes with the change in the charging current during constant-voltage charging increases, and the controller 22 can easily detect the voltage drop [-ΔV]. Thus, the full charge of the battery 14 can be reliably detected, and the charge can be stopped when the battery 14 is fully charged.

As described above, the above-described embodiment does not require a high-precision current detection circuit such as an amplifier for detecting a charging current for judging full charge, which is conventionally used, and is low in cost. A charging device capable of reliably detecting full charge and controlling charging with a simple and simple configuration is provided. In addition, with a similar circuit configuration, it is possible to charge not only a lithium ion secondary battery but also various types of secondary batteries such as a nickel cadmium battery and a nickel hydride battery. You.

[0049]

As described above, according to the present invention, the current detection circuit for detecting the charging current is not required, and the full charge of the secondary battery can be detected with a simple configuration. The present invention provides a charge control method for a secondary battery and a charging device for the secondary battery, which can reliably charge the battery fully, and can be used for other types of secondary batteries and has excellent versatility.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a charging device to which the present invention is applied.

FIG. 2 is a diagram illustrating a relationship between a charging voltage and a charging current during constant current charging / constant voltage charging.

FIG. 3 is a diagram for explaining the principle configuration of the present invention.

FIG. 4 is a flowchart showing the operation of the embodiment shown in FIG.

FIG. 5 is a graph showing a change in charging voltage and a small voltage drop [-ΔV] of a lithium ion secondary battery and another secondary battery.

FIG. 6 is a block diagram showing another embodiment of the charging device to which the present invention is applied.

FIG. 7 is a diagram showing a principle configuration in the embodiment shown in FIG. 6;

[Explanation of symbols]

 10 Charging device 12 AC adapter 14 Battery 18 Control FET 20 Charging IC 22 Controller 24 Current setting resistor (R1)

Claims (23)

[Claims] 1. A method for controlling the charging of a secondary battery that charges a secondary battery, the method comprising: controlling a battery voltage of the secondary battery and a current connected to a circuit ground in series with the secondary battery. Detecting a first voltage obtained by adding a voltage of a current setting resistor that is a setting resistor and setting a current value for the secondary battery; and changing a first voltage during charging for charging the secondary battery. Detecting whether or not the secondary battery is fully charged based on the detected voltage change, and controlling charging of the secondary battery according to the determination result. Rechargeable battery charge control method. 2. The method for controlling charging of a secondary battery according to claim 1, wherein the method includes determining whether the first voltage drops from a maximum value and determining whether the secondary battery is fully charged. And controlling the charge of the secondary battery. 3. The method for controlling charging of a secondary battery according to claim 1, wherein the method further comprises adding the first voltage and a charging path connected in series to a charging path for charging the secondary battery. Detecting a second voltage obtained by adding a voltage of a resistor, and controlling charging of the secondary battery based on the voltage change of the second voltage during the charging. Method. 4. The method for controlling charging of a secondary battery according to claim 3, wherein the method includes determining a voltage change in which the first voltage falls from a maximum value to determine whether the secondary battery is fully charged. And controlling the charge of the secondary battery. 5. The charging method for a secondary battery according to claim 2, wherein the predetermined value is selected according to a type of the secondary battery. Control method. 6. The charging control method for a secondary battery according to claim 1, wherein the charging of the secondary battery is performed by charging the secondary battery by a constant current-constant voltage charging method. A charging control method for a secondary battery, comprising: determining whether the secondary battery is fully charged at the time of charging. 7. The secondary battery charging control method according to claim 1, wherein the type of the secondary battery is determined according to a state of a switch for identifying the type of the secondary battery. When it is determined that the secondary battery is a lithium ion secondary battery, after the voltage change is detected, charging is continued for a certain period of time, and then charging is terminated. 8. The secondary battery charge control method according to claim 7, wherein the secondary battery is determined to be another secondary battery other than the lithium ion secondary battery according to a state of the switch. In some cases, the charging is terminated immediately upon detecting the voltage change. 9. The charge control method for a secondary battery according to claim 8, wherein the other secondary battery is a nickel cadmium battery. 10. The charge control method for a secondary battery according to claim 8, wherein said another secondary battery is a nickel-metal hydride battery. 11. The charging method for a secondary battery according to claim 7, wherein the predetermined time is selected according to a configuration of the secondary battery. Control method. 12. The charge control method for a secondary battery according to claim 1, wherein the charge detection method detects a voltage change from a maximum voltage to a voltage decrease. Rechargeable battery charge control method. 13. A charging device for a secondary battery for charging a secondary battery, comprising: a charging switch for connecting and disconnecting a DC power supply for charging the secondary battery to and from the secondary battery according to a control signal. A charging unit that generates a control signal for turning on / off the charging switch to control charging of the secondary battery; and a current that is connected in series with the secondary battery and sets a current value for the secondary battery. A setting resistor; and a control unit configured to detect a first voltage obtained by adding a voltage of the current setting resistor and a battery voltage of the secondary battery to determine whether the secondary battery is fully charged, Detecting a change in the first voltage during charging for charging the secondary battery, and controlling charging of the secondary battery based on the detected voltage change. Secondary battery charger. 14. The rechargeable battery charging device according to claim 13, wherein the device includes an additional resistor connected in series to a charging path for charging the rechargeable battery, and the control unit includes: And detecting a second voltage obtained by adding the battery voltage, the voltage of the current setting resistor, and the voltage of the additional resistor. 15. The secondary battery charger according to claim 13, wherein the control unit detects the voltage change by comparing the voltage change with a predetermined value for determining whether the secondary battery is fully charged. A charging device for a secondary battery, comprising: 16. The secondary battery charging apparatus according to claim 15, wherein said control means selects said predetermined value according to a type of said secondary battery. apparatus. 17. The secondary battery charging apparatus according to claim 13, wherein the charging unit performs a charging process for charging the secondary battery by a constant current-constant voltage charging method. Is a battery charger for a secondary battery, which determines whether or not the secondary battery is fully charged at the time of constant voltage charging. 18. The rechargeable battery charging device according to claim 13, wherein the device includes a switch for identifying a type of the rechargeable battery, and the control unit controls the switch according to a state of the switch. Determining the type of the secondary battery, and determining that the secondary battery is a lithium ion secondary battery, after detecting the voltage change, continuing charging for a certain period of time and then terminating the charging. A charging device for a secondary battery. 19. The secondary battery charging device according to claim 18, wherein the control unit determines that the secondary battery is a secondary battery other than the lithium ion secondary battery according to a state of the switch. A charging device for a secondary battery, wherein when it is determined that there is a voltage change, the charging is terminated immediately upon detecting the voltage change. 20. The charging device for a secondary battery according to claim 19, wherein said another secondary battery is a nickel cadmium battery. 21. The charging device for a secondary battery according to claim 19, wherein said another secondary battery is a nickel-metal hydride battery. 22. The secondary battery charger according to claim 18, wherein the control unit selects the certain time according to a configuration of the secondary battery, and elapses the selected certain time. A charging device for a secondary battery, wherein the charging is terminated later. 23. The charging device for a secondary battery according to claim 13, wherein the control unit detects a voltage change in which the voltage at the time of charging goes from a maximum to a decrease. Rechargeable battery charger.