A battery pack which includes a plurality of contact portions in a terminal accommodating portion provided in each of cell receiving portions of a plurality of battery cells, so that one selected from the plurality of contact portions can be electrically connected to electrode terminals of the battery cells even if the plurality of battery cells have different widths of wide walls. In addition, since the battery pack includes a series/parallel switch provided outside an external pack, a connection method of a plurality of battery cells provided inside the external pack can be switched to series/parallel connection. Further, since the battery pack includes a capacity display unit provided outside an external pack, capacity levels of a plurality of battery cells provided inside the external pack can be identified.