A battery pack to be mounted on a vehicle. The battery pack has a battery stack. A cooling fan, a fan relay, and a main relay (−) are disposed on one side of the battery stack. A control module, a register, a main relay (+), and a pre-charge relay are disposed on the other side of the same. As a result of devices being disposed on both sides of the battery stack, the weight of the battery pack is adjusted to the neighborhood of the center of the battery pack.