Batteries can be thought of as single-use power sources that must be disposed of after they have been used up. They are also called primary batteries because they are characterized by their size (such as AA, AAA, or 123). Typically, these kinds of batteries are used for small devices such as flashlights, remote controls, smoke detectors, occupancy sensors, light duty power screwdrivers, and other small electronic devices. In addition to this, they are able to provide backup power for devices that are predominantly powered by electricity as well.