A battery pack including a bare cell, the bare cell having a pair of first side portions opposite to each other, a pair of second side portions opposite to each other, and a pair of plane portions opposite to each other, the second side portions and the plane portions being connected to ends of the first side portions; a protection circuit module electrically connected to the bare cell; an inner frame between the bare cell and the protection circuit module, the inner frame accommodating the bare cell and exposing one side portion of the pair of first side portions; and an outer frame, the outer frame accommodating the bare cell, the protection circuit module, and the inner frame and exposing the pair of plane portions.