Safety is secured in such a manner that an anomaly of a secondary battery is detected with a protection circuit, for example, a phenomenon that lowers the safety of a secondary battery, particularly a micro short circuit, is detected early, and users are warned or the use of the secondary battery is stopped. A secondary battery protection circuit includes a first memory circuit electrically connected to a secondary battery, a comparison circuit electrically connected to the first memory circuit, a second memory circuit electrically connected to the comparison circuit, and a power-off switch electrically connected to the second memory circuit. The power-off switch is electrically connected to the secondary battery, and the first memory circuit includes a first transistor including an oxide semiconductor and retains a voltage value of the secondary battery in an analog manner.
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