A lithium battery is a long-life, lightweight, high-power battery used in watches. It is normally in the shape of a coin. As the name suggests, the battery has lithium in it. The lithium is oxidized, providing the power for the battery. They are not rechargeable; once they are dead they should be thrown out. A lithium battery is different from a lithium-ion battery. They are rechargeable and are used in phones, portable computers, and other items like that. Lithium batteries come in several sizes. The size is indicated by a code. CR1216 is a small battery, while CR2012 is medium-sized and CR2450 is large. They are normally more expensive than other batteries.