An upper base portion of a top portion of a battery cell cap functions as a positive terminal, and paths for flow of electrical current are defined between the top portion and portions for welding. The portions for welding are positioned to face a side wall region between a pair of apertures adjacently provided in the top portion, and the current flowing regions are defined between the portions for welding and the side wall regions of the top portion facing to the portions for welding, each forming a symmetrical current flowing region.