A battery pack includes: a plurality of batteries; a detection section to measure a voltage of each of the plurality of batteries to obtain a voltage variation of each of the plurality of batteries at different lapse times and compare the obtained voltage variations to thus detect whether at least one of the plurality of batteries has been replaced; and a controller to disable, when a result of the detection by the detection section indicates that at least one of the plurality of batteries has been replaced, a use of the plurality of batteries.