To prolong the life of usage of a battery by automatically exhausting heated air in a battery case, whether the battery is in a state of charging, discharging, or preservation.

Suction ports 12 and exhaustion ports 13 are arranged at either side of the sealed battery case 10, and a fan 30 is arranged at the suction ports 12 and the exhaustion ports 13, respectively. A temperature control element, the fan 30 and the battery case 10 are connected so as to form an electronic circuit, so that the fan 30 automatically operates and exhausts the heated air outward when the temperature in the battery case 10 gets to a prescribed value, whether the battery is in a state of charging, discharging, or preservation.