Editing Flashlight (section)

== Power sources ==
===Batteries===
[[File:3x AA to D battery converter, MY DAY vintage flashlight, Sofirn SP36 flashlight.jpg|thumb|Left to right: 3x AA to D parallel battery converter with rechargeable NiMH AA-size batteries inserted. MY DAY vintage flashlight. It uses 1.5 V D-size batteries. Sofirn SP36 flashlight.  It features a 5 V 2 A USB-C charging port to load 3.7 V 18650 rechargeable lithium-ion batteries.]]

The most common power source for flashlights is the battery. [[Primary battery]] ([[disposable]])  types used in flashlights include  [[button cell]]s, [[carbon zinc battery|carbon-zinc batteries]] in both regular and heavy duty types, [[Alkaline battery|alkaline]], and [[Lithium metal battery|lithium]].

The most common power source for flashlights is the battery. [[Primary battery]] ([[disposable]])  types used in flashlights include  [[button cell]]s, [[carbon zinc battery|carbon-zinc batteries]] in both regular and heavy duty types, [[Alkaline battery|alkaline]], and [[Lithium metal battery|lithium]].

Secondary, rechargeable types include [[lead-acid battery|lead-acid batteries]], [[Nickel metal hydride battery|NiMH]], [[Nickel-cadmium battery|NiCd]] batteries and [[lithium-ion battery|lithium-ion batteries]]. The choice of batteries plays a determining role in the size, weight, run time, and shape of the flashlight. Flashlight users may prefer a common battery type to simplify replacement.

Primary cells are most economical for infrequent use. Some types of lithium primary cell can be stored for years with less risk of leakage compared with zinc-type batteries. Long storage life is useful where flashlights are required only in emergencies. Lithium primary batteries are also useful at lower temperatures than zinc batteries, all of which have water-based electrolytes. Lithium primary batteries have a lower [[internal resistance]] than zinc primary batteries, so are more efficient in high-drain flashlights.

Flashlights used for extended periods every day may be more economically operated on rechargeable (secondary) batteries. Flashlights designed for rechargeable batteries may  allow charging without removing the batteries; for example, a light kept in a vehicle may be trickle-charged and always ready when needed. Some rechargeable flashlights have indicators for the state of charge of the battery. Power-failure lights are designed to keep their batteries charged from a wall plug and to automatically turn on after an AC power failure; the power-failure light can be removed from the wall socket and used as a portable flashlight. [[Solar powered flashlight]]s use energy from [[solar cell]]s to charge an on-board battery for later use.

=== Mechanical power ===
{{Main|Mechanically powered flashlight}}
One type of mechanically powered flashlight has a winding crank and spring connected to a small [[electrical generator]] (dynamo).  Some types use the dynamo to charge a capacitor or battery, while others only light while the dynamo is moving. Others generate electricity using [[electromagnetic induction]]. They use a strong permanent [[magnet]] that can freely slide up and down a tube, passing through a coil of wire as it does. Shaking the flashlight charges a [[capacitor]] or a rechargeable battery that supplies current to a light source.  Such flashlights can be useful during an emergency, when utility power and batteries may not be available. Dynamo-powered flashlights were popular during the Second World War since replacement batteries were difficult to find.

===Capacitor===
At least one manufacturer makes a rechargeable flashlight that uses a [[supercapacitor]] to store energy.<ref>Francois Beguin, Elzbieta Frackowiak (ed), ''Supercapacitors: Materials, Systems and Applications'' Wiley 2013, {{ISBN|3527646698}}, p. 515</ref>  The capacitor can be recharged more rapidly than a battery and can be recharged many times without loss of capacity; however, the running time is limited by the relative bulk of capacitors compared to electrochemical batteries.