A secondary-battery management apparatus calculates the possible discharge duration of a secondary battery correctly even after a load current changes. The secondary-battery management apparatus calculates the remaining capacity and the remaining lifetime of the secondary battery in accordance with a measured temperature of the battery in a standby state, calculates the remaining capacity of the battery in accordance with a measured discharging current of the battery while the battery is in a discharging state, and calculates the remaining capacity of the battery in accordance with a measured charging current while the battery is in a charging state. When discharging from the battery is required by means of a reduction of an output voltage of a rectifier, the deterioration of the battery is checked by discharging to a load device. A battery capacity is checked by measuring the discharge duration of the battery in the discharge by the load current pattern.