Patent ID: 7079003

Claim:
A secondary battery, comprising: a storage battery; a protective circuit; an auxiliary switch element; a heater element; a first auxiliary fuse element; and first and second output terminals, wherein: when a battery charger is connected to the first and second output terminals, a charge current supplied by the battery charger flows through the protective circuit to charge the storage battery; when an external circuit is connected to the first and second output terminals, a discharge current from the storage battery flows through the protective circuit and is supplied to the external circuit; and the protective circuit includes: a series circuit of a first resistance element, a second resistance element and a main fuse element being connected in series with each other, wherein the series circuit is connected between a high-voltage output terminal and a low-voltage output terminal of the storage battery, the voltage between the high-voltage output terminal and the low-voltage output terminal is divided by the first resistance element and the second resistance element to generate a divided voltage before blowout of the main fuse element, the divided voltage is inputted to the auxiliary switch element so that the auxiliary switch element is in an OFF state, the auxiliary switch element is connected to the high-voltage output terminal or the low-voltage output terminal by the first or second resistance element so as to be brought into an ON state when the main fuse element is blown by heat generated at a temperature sense portion, the heater element is allowed a current to flow therethrough when the auxiliary switch element is turned ON to generate heat; and the first auxiliary fuse is blown by heat generated by the heater element, and disconnects the first output terminal from the storage battery and the heater element.