High Quality Content by WIKIPEDIA articles! A watch battery or button cell is a small single cell battery shaped as a squat cylinder typically 5 to 20 mm in diameter and 1 to 6 mm high—like a button on a garment, hence the name. Button cells are used to power small portable electronics devices such as wrist watches, pocket calculators, and hearing aids. Some cells larger than the dimensions above are also called button cells, but are less commonly used. Lithium cells are generally similar but somewhat larger; they tend to be called either lithium cells or batteries or coin cells rather than button cells.