A secondary battery having a compact design by using planar lead plates. In the secondary battery, a third lead plate is arranged on a top side of a protective circuit module, while the first and second lead plates are planar and are arranged on a bottom side of the protective circuit module. Therefore, a coupling height of a bare cell to the protective circuit module can be minimized to allow for an increased capacity of the bare cell. The protective circuit module may include an accommodation portion, such as a groove or a through hole, to accommodate a plug of an electrolyte injection hole in the cap plate.