Infinite Flashlight

So it's the middle of the night, you're being chased by mangled oversized toddlers with knives through a Kafkaesque take on a dark and twisted elementary school, and you realize that in all the chaos you've completely forgotten to change the batteries in your flashlight. Sounds like a problem, right? Wrong!

You have an Infinite Flashlight, which will never run out unless the plot dictates otherwise. If need be, you could probably hook it up to an inverter and power a city from the bottomless depths of your flashlight (if it wouldn't rob you of your only light source while you worked, remember those knife-babies?).

Of course, many games don't take enough in-game time to complete for four D-cells of battery power to run out. But even if you can take weeks or even months to complete the main plot, the flashlight will never run out. Definitely an Acceptable Break from Reality. Such things do exist in some form in real life, but typically require shaking to provide kinetic energy to charge a capacitor to power a feeble white LED (granted, you're probably shaking hard enough as it is because of the fiendish killer knife babies). More usefully, "survival" flashlights use a crank mechanism and generator to recharge a battery, which is powerful enough to power medium-power LEDs.

Contrast with Ten-Second Flashlight, the usual result when developers try to avert this one.

Action Game

 * Dante from Devil May Cry uses a nugget of Luminite as a makeshift lantern in the first game, and the light never fades.

Action Adventure

 * The Legend of Zelda a Link To T He Past has a lantern that consumes magic to light Ten-Second Flashlight torches, but always lights up the area in front of you just fine.
 * This was changed in The Legend of Zelda Twilight Princess, where the lantern needs oil. Thankfully it doesn't run out Ten-Second Flashlight-fast.
 * On the other hand, Zelda II the Adventure of Link was even worse: once you get the Candle, all dark caves in the game are automatically lit, through and through. You don't even have to select it.
 * Luigi's flashlight in Luigis Mansion never runs out throughout the entire game. Admittedly, the game isn't supposed to take that much time, but you still use the flashlight a whole lot.

Adventure Game

 * In Adventure (the text game from 1976) your first set of flashlight batteries will run out fairly quickly. After you replace them, the fresh batteries last forever.
 * The obscure 1984 computer game Below the Root (based on Zilpha Keatley Snyder's Green-Sky Trilogy) had an underground area that was pitch-dark. It was possible to obtain honeylamps that would provide light for a short time, but to fully explore the area and beat the game, it was highly recommended that you obtain an item called the spirit lamp, which provides light for as long as you hold the item.
 * Possibly justified in Rama, which takes place in the distant future. Arthur C. Clarke did hope that we would tap into zero-point energy someday.

First Person Shooter

 * Left 4 Dead. So why do you have the ability to turn it on and off? Stealth. Sometimes it's easier to sneak past the Commons, and it always is in the Witch's case.
 * Doom 3. The in-game description even says that it has a static power source. It does get knocked out at one point in the game by some annoying electromagnetic pulses, but it's a temporary thing and it only happens twice, when you are not in immediate danger.
 * In Bungie's Pathways into Darkness, you only have five days to complete your mission before the Sealed Evil in a Can awakens to destroy ordered reality on earth, your flashlight can last for a week. Although there is a set of nightvision goggles necessary to get past evil creepy-crawlies that are attracted to your flashlight.
 * The Chronicles of Riddick: Escape From Butcher Bay, at least before you get the titular character's 'eyeshine' ability.
 * Except for one level--and what a level it is. At one point, Riddick tackles a guard, dropping both of them down a very, very deep well and into the sewers. Riddick thus loses all his weapons and is forced to use the guard's shotgun. The shotgun has a built-in flashlight, as do most of the weapons, but it's been damaged in the fall and flickers continuously. What's more, it'll fail completely in exactly eight minutes, as the computer voice (in the shotgun) helpfully informs you. So you're down in the deep, dank sewers with only a few minutes until you're left in the dark forever. Oh, and did I mention the crazy sewer mutants who pop out of nowhere?
 * Averted in the first Halo game, where the flashlight can indeed run out. The flashlights in Halos 2 & 3, however, are infinite, though this is handwaved as drawing power from your new suit's fusion core. It will however turn off on its own in lighted areas.
 * F.E.A.R. had a rather annoying Ten-Second Flashlight. The sequel, Project Origin, instead uses an Infinite Flashlight that specifically fails during supernatural scare sequences.
 * Team Fortress Classic still has the flashlight from Half-Life 1 in the code, but because the power gauge was removed it now shines indefinitely. If you're curious, you activate it by hitting the ~ key and typing: bind "impulse 100"
 * In The Nameless Mod using a (somewhat rare) augmentation upgrade on your default light enhancement results in this. As a Deus Ex mod (where gameplay pretty much required dark areas), this comes in handy.
 * In BioShock (series) 2, your suit will automatically turn on in dark areas. Given that you're playing a not-quite-human thing that can change what color its body to express its mood, it's less of an "Infinite Flashlight" and more of "Making Yourself More Bright When You Need It".
 * In Vietcong the player has a flashlight that never runs out of power - mainly useful for the mission segments when you must traverse through the tunnel systems of your enemies. However, some players never actually realised they had a flashlight during those missions since they'd never used it previously and ended up negotiating the tunnels in near complete darkness. A case of read the manual in those cases.
 * STALKER gives you a infinite headlamp by default. Some of the higher-end suits have really crappy, but unlimited, night vision.
 * Metro 2033 takes a surprisingly realistic approach: the flashlight runs on batteries that need to be periodically recharged by a crank mechanism. You can keep cranking past 100% charge to temporarily make the light brighter.
 * Unreal has a powerful, permanent "searchlight" that you get far into the game (which makes you use a good number of disposable versions before that point), which is not in fact infinite. Its charge is so high no sane player is likely to run out of power for it, but if you take long enough to finish the game it's likely you'll see its charge bar diminish a fair bit before the end. Makes no difference in gameplay terms, though, so it counts as playing it straight.
 * Painkiller and its expansion, Painkiller: Battle out of Hell both have infinite flashlights. In the first game it is literally a flashlight that emanates inexplicably from Daniel's chest (you never see the light itself, but it does flicker, make electrical noises and has a distortion in the center like a normal flashlight). in Battle out of Hell, the light has been replaced with a strange glowing yellow ball in the bottom left corner of the screen. Presumably, this is supposed to represent a lantern or candle instead of an electrical torch.

Platform Game

 * Squawks in the first Donkey Kong Country and Glimmer in the second.

Roguelike

 * In Nethack, lamps and candles are available as quite rare light sources. Now normal ones burn out eventually (though lamps can be recharged with a potion of oil), but Magic Lamps last forever. Likewise, the Spell, Scroll, and Wand of Light create permanent fields of light.

Role Playing Game

 * The Pip-Boy 3000a wrist computer in Fallout 3 can also be used as a lantern with an unlimited power supply. Justified by the prevalence of miniaturized nuclear and fusion power.
 * Interestingly, it's not a flashlight per se. The character just turns on the backlight for the screen.
 * An interesting variation: In SaGa 2 there's a cave where it's too bright to see anything inside, aptly named Bright Cave. You need the TrueEye MAGI to see normally in the cave, but it never wears off, making the MAGI an Infinite... Flashdark?
 * Mass Effect 3 gives the crew muzzle flashlights, but it's plausible to presume they're run off whatever absurdly high-capacity battery is flinging minuscule slugs at absurd muzzle velocities all day out of the gun, and they're never on for very long anyway.

Survival Horror

 * Every game in the Silent Hill series, although in Silent Hill 2, the battery would occasionally die when the plot called for it.
 * In Silent Hill 2, the battery died twice, once when you enter a specific room late in the game, and the other happens even later - thankfully, the environment is lit up enough for you to see just fine.
 * One of the last chapters in Eternal Darkness has a character with one of these. To be fair though, he's a firefighter, so it's probably less "infinite" and more "heavy duty" (or, as the game calls it, "equiped with long-endurnce battery"). Either way, if you sit in a safe room with it on, and then just leave the game running for days, it'll still be happily shining when you come back.
 * Used throughout the Fatal Frame series. The one exception occurs in the second game, when the flashlight's temporary failure is used to indicate that there's something very wrong with the particular house the protagonist has entered.
 * Dead Space 2: Isaac's plasma cutter in actually a flashlight combined with a surgical tool that keeps working no matter how many zombies he beats to death with it.

Third Person Shooter

 * All of the Syphon Filter games.

Other

 * The Who Framed Roger Rabbit? game for the NES -- sort of. For some reason, you have to use a different flashlight in each cave, but those caves stay lit permanently. And all over.

Web Original

 * Discussed in Cracked: Photoplasty advertises it in Ads for Products That Must Exist in Video Games.