The invention provides a rechargeable battery pack including a unit battery cell; a frame surrounding perimeter sides of the unit battery cell; a protective circuit module electrically connected to the unit battery cell and supported within the frame; and a pair of case members coupled to the frame and covering respective first and second sides of the unit battery cell, the first and second sides being opposite each other, and the frame includes a circuit installation part at a side of the frame and supporting the protective circuit module.