Both mechanical and electronic watches require a power source for it to run. In a mechanical watch, power is provided by the use of a spring called the mainspring. It has to be wound periodically. An improvement was developed in which the watches were self-winding. They are called automatic watches which depended on the wearer’s hand movements to power the spring.

More common and less expensive electronic watches are powered by electricity. This comes from different kinds of cell batteries that are precisely made for this purpose. They are small and provide tiny amounts of power continuously for long periods of time. They commonly contain zinc or lithium. An alkaline watch battery will provide less capacity than lithium cells. A more recent development is the creation of the solar watch. It is powered by sunlight that is processed and stored in a different kind of battery.