To appropriately control serially connected batteries.
When checking an output voltage of a secondary battery E1, a capacitor C1 is charged by the secondary battery E1 with only SW1 and SW2 turned on. After an elapse of time of ΔT, SW1 and SW2 are turned off and SW4 and SW5 are turned on to move the charge of the capacitor C1 to a capacitor C2. When the potential of the capacitor C2 becomes nearly equal to the output voltage of the secondary battery E1 by repeating of the above operation, a potential of the capacitor C2 is detected by a voltage detector 11. As one side of the capacitor C2 is connected to a ground potential, the voltage can be stably detected. The capacitor C2 is charged by a secondary battery E2 with only SW5 turned on, and the potential of the capacitor C2 is detected by the voltage detector 11. As the voltage detector 11 is commonly used for the secondary batteries E1, E2, fluctuation of detection is eliminated. Further, by utilizing above method, it is possible to supply a circuit power source by the capacitor C2.
YAMAZAKI KAZUO
AKIYASU HITOSHI
IKEDA TAMON
Koichi Mori