A battery was a device which stored 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 Twelfth Doctor accused an Aranox stranded on Earth of using humans as batteries, as it was extracting their psychic energy to restock its ship's fuel reserves. (COMIC: Unearthly Things)
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)
In the early 21st century, the Ninth Doctor bought a battery for his mobile phone from Antonio Spinozzi. By 2005, AA batteries were found on Earth. (PROSE: Have You Seen This Man?)
In 2007 in Pete's World, one of the potential solutions provided by IE ATSS to fix ChatGuest1's broken radio was to change the batteries. (GAME: Cybus Spy)