Abstract: A protection circuit device for protecting a secondary battery from an overcharge and/or an overdischarge has first and second terminals, across which a charger and a load are alternatively connectable. A first switch and/or a second switch may be provided in series with the secondary battery between the first and second terminals. In a charging operation mode, the second switch is kept conductive. A charging operation is performed with the first switch made conductive. When the battery is overcharged for some reasons, the first switch is turned off. Upon connection of a load across the first and second terminals, the first switch is restored to a conductive state for a discharging operation which releases the battery from an overdischarge state. In a discharging operation mode, the first switch is kept conductive. A discharge operation is performed with the second switch made conductive.