The safety is ensured in such a manner that an abnormality of a secondary battery is detected, for example, a phenomenon that lowers the safety of the secondary battery is detected early and a warning is given to a user. A first protection circuit and a second protection circuit are provided for one secondary battery. The first protection circuit includes a memory circuit including a transistor including an oxide semiconductor. Combination of a plurality of protection circuits enables a complementary double protection system in charging, and the safety can be further enhanced.