A secondary-battery protection circuit is configured to, in response to detecting that a first switching circuit is turned on and a second switching circuit is turned on, supply a first output voltage to a first load between a first terminal and a second terminal; and supply a third output voltage to a second load between the first terminal and a third terminal, the third output voltage indicating the sum of the first output voltage and a second output voltage, the second output voltage corresponding to a voltage across a second secondary battery. In response to detecting that the first switching circuit is turned off and the second switching circuit is turned on, the secondary-battery protection circuit is configured to stop supplying the first output voltage to the first load; and stop supplying the third output voltage via the first terminal and the third terminal.