What is a Button Battery (Button/Coin Cell Battery)?

A button cell battery (alternatively also known as a coin cell battery) gets its name because they resemble small buttons. Button cells are used to power small portable electronics devices such as wrist watches, pocket calculators or hearing aids. Stainless steel usually forms the bottom body and positive terminal of the coin cell battery; insulated from it, the metallic top cap forms the negative terminal. Devices using button cells are usually designed around a cell giving a long service life, typically well over a year in continuous use in a wristwatch. Most button cells have low self-discharge, holding their charge for a long time if not used.