A battery pack includes: a plastic-made, elongated outer casing composed of interconnected peripheral walls to define an interior battery storage portion; and a battery accommodated in the battery storage portion inside the outer casing. The outer casing has a mounting protrusion to be attached to and project outwardly from an electronic equipment casing. An inner casing is incorporated inside the outer casing of the battery pack. The battery pack is constructed and arranged so that an outer battery, located outside the electronic equipment, is accommodated inside the inner casing.