A battery was a device to store energy.
According to Ace, a crude battery had been discovered in what had been Mesopotamia. The Seventh Doctor speculated that it was one of Ishtar's prototypes. (PROSE: Timewyrm: Genesys)
K9 ran on an electron-fusion nuclear battery. (PROSE: Housewarming)
The colonists on Frontios used acid jars as batteries. (TV: Frontios)
Penelope Gate's time machine was powered by a mutated Tzun battery. (PROSE: The Room With No Doors)
Fission cell batteries were used on Red Rocket Rising. They were cheap and efficient, but very volatile. (AUDIO: Blood of the Daleks)