Battery, Electric, a device that produces electric current without the use of moving parts. Strictly speaking, a battery consists of two or more electric cells connected electrically to provide a single source of electricity. However, in common usage, the term battery is also applied to single, self-contained cells such as those used in flashlights and electronic watches.

Batteries are a source of direct current (DC). They are widely used to supply electricity for equipment ranging in size from hearing aids to automobiles, and to provide power for portable equipment and equipment at remote locations. Batteries are generally impractical, however, for large-scale uses, such as lighting streets and houses.

Cells that provide electricity by transforming chemical energy into electrical energy are called galvanic, or voltaic, cells. There are two major types: primary cells and secondary cells. A primary cell is one that requires replacement once the materials it contains are used by the chemical reactions that take place in the cell. With a secondary cell, the chemical reactions can be readily reversed to restore the materials used up in the cell. Secondary cells form the basis of storage batteries. A third type, called a fuel cell, uses outside materials that are continuously supplied to the cell.

Cells that convert the energy of visible light into electricity are called photovoltaic, or solar, cells. Thermoelectric cells produce electricity from heat energy; nuclear batteries produce electricity from the radiation emitted by radioactive substances.