A battery pack is provided. For example, the battery pack includes a box-shaped or plate-shaped battery pack. The battery pack has a hard outer jacket member, a box-shaped or plate-shaped battery element, a cover, and a circuit board. The hard outer jacket member has a first opening and a second opening formed at both ends. The box-shaped or plate-shaped battery element is contained in the outer jacket member and has electrode terminals. The cover is molded from resin and is fitted to the first opening. The circuit board is connected to the electrode terminal leads and contained in the cover. At least the electrode terminal leads extends from the first opening. The cover has concave portions on both ends of one longer side. The outer jacket member has cut portions that expose at least the concave portions of the cover. At least a longer side of the cover and the outer jacket member are heat-adhered.