BATTERY

A battery includes a battery cell and a terminal post. The first casing includes a first arc sidewall and a flat sidewall connected to the first arc sidewall and the first sidewall. The terminal post is disposed on the flat sidewall. Instead of disposing the terminal post on top of the battery, increased thickness of the battery due to the terminal post is avoided in the present disclosure. The internal space of an electrode device can be fully utilized. In addition, it can prevent the terminal post from occupying the top of the battery and decreasing the number of the electrode plates. Thus, the present disclosure can avoid the reduce of the number of the electrode plates and increase the energy density of the battery.