Patent ID: 7565165

Claim:
A telephone comprising: a telephone main unit incorporating a battery; and a charger that supplies power to the telephone main unit and the battery, the telephone main unit comprising: a chargeable state determination unit that determines whether or not the telephone main unit is in a chargeable state in which the telephone main unit is supplied with power by the charger; a standby state determination unit that determines, when the chargeable state determination unit determines that the telephone main unit is in the chargeable state, whether or not the telephone main unit is in a standby state; a battery voltage detection unit that detects voltage across input and output sides of the battery; a voltage determination unit that determines, when the standby state determination unit determines that the telephone main unit is in the standby state, whether or not the voltage detected by the battery voltage detection unit exceeds a threshold voltage set based on a voltage when the battery is normally connected; a warning unit that issues a warning to the effect that power cannot be supplied from the battery when the voltage determination unit determines that the detected voltage exceeds the threshold voltage; a threshold voltage correction unit that corrects the threshold voltage; and a correction value storage unit that stores the corrected threshold voltage as the threshold voltage.