Living Battery

Most Magitech and machines require some kind of Power Source. Common sources are coal, steam, electricity, or even Phlebotinum. But sometimes, that source is something which is biological and alive, sometimes even sentient. It's a Living Battery, which the machine or device takes the Life Energy from almost parasitically.

We generally don't feel too bad if such living batteries are plants or insects, but the more intelligent, humanoid and sentient the creature, the more likely this will be Played for Drama. The story may reveal the battery is being taken advantage of, if not outright enslaved, and the extraction of the Living Battery's energy is harmful, traumatizing, or even lethal. Often the justification for why it is necessary is some form of Higher-Species-Rights, Fantastic Racism, the fact that the parasitic species created the Living Battery in the first place, or simple desperation and need on the part of the extracting species. Or the extractors might just be Villains who don't care who they hurt in the name of gaining power.

A Sub-Trope of Power Source. Powered by a Forsaken Child is itself a subtrope. Compare Life Energy, Sentient Phlebotinum, Human Resources and Cast From Hit Points.

Anime And Manga

 * In Trigun, the people couldn't survive on Gunsmoke without the plants, giant humanoid alien things that were placed in equally giant bulbs from which energy was extracted, which powered just about everything.
 * The machines in Kakurenbo use the children they captured for this.
 * The Batteryman and Gadget cards from the Yu-Gi-Oh! Trading Card game. They also appear in the series finale of Duel Monsters, as well as Yu-Gi-Oh! 5D's.
 * Sailor Moon villains, especially Alan and Ann, quite often extract some sort of energy directly from human victims to supply to awakening some evil Big Bad.
 * Black Bird has this, with a twist. The living battery (the heroine) isn't harmed by having her energy used. She just gives it off like a fire gives off heat. Though the other things that she can provide aren't nearly as non-invasive to harvest...

Comics

 * The Uncanny X-Men: When the group first discovered the island of Genosha, they discovered that mutants had been enslaved to increase the quality of life for the human citizens. One mutant was used as a living power source for the monorail-like mass transit vehicle that he piloted.
 * In BPRD: Hollow Earth, The King of Fear has Liz Sherman kidnapped so he can use her life force to power his war mechas.
 * In All Fall Down, the Order of Despots kidnaps the superhero Isotope to use him for this very purpose.
 * In the story "Fountains of Youth", in issue #22 of The Vault of Horror, an elderly woman that went through a series of young female companions turned out to be a centuries-old creature that was sucking the life force from them.

Film

 * The machines in The Matrix were powered by a mixture of fusion and the energy produced by humans which they grew and harvested in fields like livestock or produce.
 * eXistenZ: The biological game device runs on the energy of the user, since it plugs directly into a "bioport" (sort of an extra anus artificially installed in the lower back). It's suggested that all gaming devices operate the same way.
 * In Final Fantasy the Spirits Within some of the weapons and equipment used organic power cells containing bacteria from which "Bio-etheric energy" was extracted.

Literature

 * The best devices of The Tommyknockers were powered by lifeforce.
 * "Lose Now, Pay Later" by Carol Farley has aliens who powered their tech with human fat from special slimming machines they invented--and to ensure an adequate supply, they also came out with some beverage that was irresistibly delicious but also super-fattening.
 * One of the dark secrets of Tad Williams's The War of the Flowers is that, with Oberon and Titania gone, the world of Faerie is drawing its power from . It's only a secret to Theo and the audience, though. The world of Faerie knows and hates it.
 * In the Doctor Who Virgin New Adventures novel Time's Crucible, a prototype Gallifreyan time capsule is powered by the psychic energies of its crew. "Battery" is an official title of one of the crew.
 * In the Ravenloft novel Dance of the Dead, a magical riverboat turns out to be powered by magical creatures and benign spirits imprisoned in its hold.

Live Action TV

 * The titular "beast" from the Doctor Who episode "The Beast Below". It was revealed that
 * In the fourth season of Buffy the Vampire Slayer, there was an episode where Buffy and Riley were living batteries in a frat house via nonstop sex.
 * In the Star Trek: Voyager episode Equinox, like Voyager, the Equinox had found itself trapped in the Delta Quadrant. In order to get home, it had discovered a faster way to get home by torturing the alien of the week. Janeway was not pleased.
 * Occurs accidentally in Farscape when a Luxan priestess needs D'Argo's help to perform her death ritual, but chooses instead to make herself younger when she realizes how strong he is. Turns out she was actually sensing and stealing Moya's life energy.

Tabletop RPG

 * Dungeons and Dragons. The Spelljammer campaign setting had Lifejammer and Death Helms, which powered their ship's flight by draining the Life Energy of the victim strapped into them (in game terms they drained Hit Points).
 * In Genius: The Transgression, Geniuses can take the merit "Calculus Vampire" which allows them to drain mania from living creatures (or other things). Manes also have the ability to do so automatically.
 * Dark Conspiracy supplement Darktek. A number of the Dark Minion items can only be recharged by draining the user's Life Force.
 * Shadowrun. Most cyberware is powered by the owner's bioelectric energy.

Web Comic

 * The webcomic Machine Gun Angel has the Mega Corp who took over the world After the End running power plants on energy harvested from genetically manipulated humans (originally, they used sentient human clones, but they caved to public pressure and made clones that were Empty Shells).
 * The Psiioniic from Homestuck was forced to Cast From Hit Points to fuel the Condense's intergalactic ship.
 * In Girl Genius, Agatha drinks water from the Dyne and is super-charged as a temporary power source.
 * In Breakfast of the Gods, Cookie Jarvis the Wizard forsaw the coming of Count Chocula and his forces and needed someone pure of heart to act as a battery to boost Cerelia's defenses. This turns out to be the reason : he volunteered to be the battery.

Video games

 * The badniks of early Sonic the Hedgehog games were powered by little animals, making it Sonic's mission to destroy them, freeing his friends inside. This played a large (and tragic) part in E-102 Gamma's story in Sonic Adventure.
 * In Shadow the Hedgehog, Black Doom wants to use humans as a power source instead.
 * In the Mega Man Zero series, Cyber Elves are sentient beings of energy that will sacrifice themselves to the benefit of the player. The nurse types specifically are converted into usable energy. The Dark Elf is the only one that is used as a continuous power source without dying.
 * In Mario and Luigi Partners In Time, the Shroobs use Toads to power their flying saucers. A used-up Toad turns into a small purple (ordinary) mushroom.
 * In Ecco: Defender of the Future, there's a level in the evil version of the future where evil dolphins are using humpback whales as a living power source.
 * In Quake IV, we discover just what produces the energy that the Strogg use: human corpses in various stages of mutilation, attached to the machinery they power. Near the end of the game, the player himself has to activate the distribution of these to power up a certain facility.
 * While they don't require one to operate, from Solatorobo will turn you into one in exchange for controlling them.

Visual Novel

 * The Synchronizers in Tsukihime, e.g., are living magical batteries that can accumulate and transfer life energy to other people, such as.

Western Animation

 * In Generator Rex there's a whole country that gets its electricity from a single EVO.
 * The Secret Saturdays once visited a small nation that got its power from two imprisoned cryptids. What's more, they're baby cryptids, and momma isn't happy about it.
 * The Venture Brothers has a Mr. Fantastic knockoff using the flames of their Human Torch knockoff to power his entire facility.
 * In Ben 10, Max met his future wife Verdona when a group of aliens meant to use her (an Energy Being) as a power source, which would be painful and eventually kill her.