电池，一般狭义上的定义是将本身保存的化学能转成电能的设备，广义的定义为将预先保存起的能量转化为可供外用电能的设备。因此，像太阳能电池只有转化而无保存功能的设备不算是电池。其他名称有电瓶、电芯，而中文池及瓶也有保存作用之意。

英文中，单一个电池结构叫做「Cell」（单电池），内部有多个Cell并连或串连的结构叫做「Battery」（电池组）。市售一般干电池其实构造上是「Cell」但英文上习惯称「Battery」，汽车用铅酸电池与方形9V电池则是真正的「Battery」。

An electric battery is a device consisting of one or more electrochemical cells with external connections provided to power electrical devices. A battery has a positive terminal, or cathode, and a negative terminal, or anode. The terminal marked positive is at a higher electrical potential energy than is the terminal marked negative. The terminal marked negative is the source of electrons that when connected to an external circuit will flow and deliver energy to an external device. When a battery is connected to an external circuit, electrolytes are able to move as ions within, allowing the chemical reactions to be completed at the separate terminals and so deliver energy to the external circuit. It is the movement of those ions within the battery which allows current to flow out of the battery to perform work. Historically the term "battery" specifically referred to a device composed of multiple cells, however the usage has evolved to additionally include devices composed of a single cell.