A rechargeable battery pack includes a frame accommodating a unit cell including a rechargeable battery; a protection circuit module electrically connected to the unit cell and in the frame; and a pair of cases coupled to opposite sides of the frame and accommodating the unit cell and the protection circuit module, and wherein the frame has coupling grooves in the sides and wherein each of the pair of cases comprises coupling protrusions, the coupling protrusions of each case being alternately coupled to the coupling grooves.