The invention discloses a battery pack. A rechargeable battery pack includes a plurality of unit cells, a protection circuit module, flexible printed circuit boards, and a case. The plurality of unit cells are comprised of a rechargeable battery and divided into a first group of unit cells and a second group of unit cells. The protection circuit module electrically protects the unit cells. The flexible printed circuit boards connect the unit cells to the protection circuit module. The case is equipped with the unit cells, the protection circuit module and the flexible printed circuit boards. The flexible printed circuit board forms a concave groove retracting corresponding to a positive electrode lead tab or a negative electrode lead tab in one of the first group of unit cells and the second group of unit cells, and include a bending part corresponding to the concave groove.