Provided is a secondary battery in which an insertion hole where an electrode terminal is insertable is defined in a center of a bottom case disposed under a can to connect batteries to each other in series. The secondary battery includes an electrode assembly including a positive electrode tab and a negative electrode tab, a can in which the electrode assembly is received, an insulation case inserted into a top opening of the can, the insulation case having a first hole and a second hole through which the positive electrode tab and the negative electrode tab pass, a protective circuit module disposed on the insulation case, the protective circuit module being electrically connected to the positive electrode tab and the negative electrode tab, and a cap assembly including a cap plate disposed on the protective circuit module to close the top opening of the can, the cap plate being electrically connected to the protective circuit module and an electrode terminal inserted into a through hole defined in the cap plate.