A battery pack includes stacked battery cells, each battery cell including a first outer surface having an electrode tab protruding therefrom and a second outer surface that is a side surface intersecting the first outer surface, and a first case that surrounds the battery cells along the first outer surface and the second outer surface. An opening exposing the electrode tab is formed in the first case. The opening includes an inner surface that faces a side surface of all of the electrode tabs exposed through the opening and that is capable of abutting against the electrode tabs when the battery cells are inserted in the first case.