ANOMALY DETECTOR IN MOSFET SWITCHING ELEMENT AND METHOD FOR DETECTING ANOMALY

An abnormality diagnostic device and method for a MOSFET switch element included in a rechargeable battery pack is provided that makes it possible to determine whether there exists a short circuit abnormality (fusion) in a MOSFET switch element that causes a charge current to flow in. An on/off controller 107 turns off a MOSFET 102a that causes a charge current to flow into a battery module 101, a start-of-charge instruction unit 108 transmits, to a charger 200, an instruction signal to start a charging operation, and a short circuit abnormality diagnostic unit 109 determines, on the basis of an output signal of a current sensor 110, whether current is flowing through the MOSFET 102a due to the charging operation of the charger 200, so as to diagnose a short circuit abnormality in the MOSFET 102a on the basis of a result of the determination. Further, after the diagnosis of the MOSFET 102a, a diagnosis of a short circuit abnormality in a MOSFET 102b that causes a discharge current to flow out of the battery module 101 is performed, and then a diagnosis of a short circuit abnormality in a charge relay 104 is performed.