The charging current value in the first trickle charge after the rapid charge is differentiated from the charging current value in the second and subsequent trickle charge. Thus, for example, in the first trickle charge, charging can be performed with the charging current value required to simultaneously activate and charge an inactive battery. In the second and subsequent trickle charge, charging can be performed with the charging current value required to compensate for self-discharge of a rechargeable battery. By charging the battery with the charging current value required to compensate for self-discharge of the battery in the second and subsequent trickle charge, power consumption required to charge the battery can be reduced, compared to the case where the trickle charge is continued with a constant charging current value required to simultaneously activate and charge the inactive battery, as the conventional device.