Abstract: A battery pack BP having terminals T1, T2, and T3, a detecting circuit, a signal generating circuit, a temperature, voltage, and current detecting circuit, a switching circuit, and a secondary battery connected to the switching circuit. A first external signal generating unit may be connected to terminals T1 and T2 and a second external signal generating unit may be connected to terminals T2 and T3. The detecting circuit detects whether the first or second external signal generating units has been connected. In so doing, the detecting circuit may detect an impedance of the first external signal generating unit and may detect a terminal voltage of the second external signal generating unit. The on/off operations of the switching circuit SW may be controlled in accordance with the detection result.

Abstract: A battery pack BP is constructed by terminals T1, T2, and T3, a detecting circuit 1, a signal generating circuit 2, a temperature, voltage, and current detecting circuit 3, a switching circuit SW, and a secondary battery BT. An external signal generating unit 4 is connected to the terminals T1 and T2. An external signal generating unit 5 is connected to the terminals T2 and T3. The detecting circuit 1 detects that the external signal generating unit 4 or 5 has been connected. The on/off operations of the switching circuit SW are controlled in accordance with a detection result. The temperature, voltage, and current detecting circuit 3 detects a temperature of the battery pack BP and a terminal voltage and a current of the secondary battery BT. The on/off operations of the switching circuit SW are controlled on the basis of the detected temperature, voltage, and current. A signal is supplied to the signal generating circuit 2 on the basis of the detected temperature, voltage, and current.