Patent ID: 7163757

Claim:
A secondary battery comprising: a rechargeable/redischargeable accumulator; and a protective circuit connected to the accumulator wherein charging/discharging current of the accumulator flows through the protective circuit, the protective circuit comprising: a heater; a diode connected in series with the heater to form a diode-heater series circuit, the diode being forward-biased when a charging current is supplied from an external DC voltage source to the accumulator; a thermistor connected in parallel with the diode-heater series circuit, the thermistor having a resistance value increasing with temperature rise; and a fuse connected in series with a parallel circuit comprising the diode-heater series circuit and the thermistor, the fuse is adapted to break based on a selected amount of heat generated by the heater, wherein a resistance value of the heater is higher than that of the thermistor at normal temperature, and wherein the resistance value of the thermistor becomes higher than that of the heater when the thermistor is heated by the accumulator, which warms up under an overcharged condition, thereby a current flows through the heater via the diode to generate heat.