A battery pack with a simple configuration and construction that is capable of preventing the manufacture of remodeled battery packs is provided. The battery pack has a plurality of secondary batteries and a detection circuit. Each secondary battery is given an identification marker beforehand and, when the plurality of secondary batteries are separated into a first secondary battery group comprising secondary batteries selected from the plurality of secondary batteries and a second secondary battery group comprising the remaining secondary batteries not belonging to the first secondary battery group, the detection circuit creates a first data string relating to the secondary batteries that comprise the second secondary battery group, based on a prescribed calculation rule, from the identification markers for the secondary batteries that comprise the first secondary battery group, and after checking the identification markers for the secondary batteries that comprise the second secondary battery group and obtaining a second data string, compares the first data string and the second data string and, if said strings do not match, stops the functions of the battery pack.