<P> Another common type is the windup or crank - powered flashlight, with the light powered by a battery which is recharged by a generator turned by a hand crank on the flashlight . One minute of cranking typically provides about 30 to 60 minutes of light . It has the advantage that it doesn't have to be pumped continually during use like the dyno torch or some shake flashlights . However it may be less reliable as an emergency light, because the rechargeable battery it contains eventually wears out . The lithium - ion cells used are typically rated for around 500 charges . </P> <P> In an alternative "Clockwork Torch" design, produced by Freeplay Energy, the energy is mechanically stored in a flat spiral wound mainspring, rather than a battery . The owner winds the spring up by turning the crank . Then when the light is turned on, the spring unwinds, turning a generator to provide power to run the light . The purpose of this design, originally invented for use in the developing world, was to improve its reliability and useful lifetime, by avoiding or reducing reliance on a battery . As of 2012, the original design is no longer made, but updated smaller hand - cranked models using LEDs are available . </P> <P> Some mechanically powered flashlights include additional functions and features beyond just a source of light . Models sold as emergency lights have additional functions useful in emergencies, such as flashing red or yellow lights for roadside emergencies, sirens, and AM / FM, weather or shortwave radios . They may also include alternative means of charging the battery, such as an AC adaptor, solar cells, or cords that plug into a car cigarette lighter socket . </P> <P> Crank powered flashlights often have radios and other features . One popular feature is a 5 - volt USB charging port for recharging cell phones when an outlet is not available . The quality and long - term reliability of these devices vary over a wide range, from high - reliability mil - spec emergency equipment down to one - time - use non-repairable disposables </P>

Which form of energy does a battery powered flashlight receive as an input