Fission Battery (Fallout 3)

A fission battery is a miscellaneous item in Fallout 3 and Fallout: New Vegas.

Functionality
The name "fission battery" seems to imply that the device's functionality is somehow linked to the process of nuclear fission, which is used to generate electrical energy. Even though the exact workings of this item are never explained, it demonstrates the obsession of the pre-War American society of the Fallout universe with nuclear technologies replacing normal tech (see also: Divergence). However, it is worth noting that even at the level of pre-war technology in the Fallout Universe it would still be incredibly difficult to harness full blown fission at such a small scale. As such, it is likely that the fission battery is simply a form of RTG instead of a tiny nuclear reactor. As the batteries can often be found in robots, they seem to be their primary energy source. After more than 200 years of inaction, some of the robots can be reactivated, demonstrating that the batteries are a very reliable form of energy storage.

In post-war society, the fission battery has taken on the role of an on-hand generator. Throughout the Mojave Wasteland, fission batteries can be found in New Vegas streets, remote shacks in the wastes, and reoccupied suburban homes. They are used for powering a wide range of devices, like street lamps, electronic signs, light-bulbs, and other household appliances, while being easily scavenged from the common robot or appliance store, making it invaluable to the common wastelander in the absence of a reliable power grid, if any.

Fallout 3
Fission batteries are located throughout the Capital Wasteland, The Pitt, Point Lookout and Adams Air Force Base, usually in toolboxes or destroyed robots.
 * 19 on shelves and counters in the Franklin Metro utility west rooms.
 * 9 are located in Pinkerton's lab in the broken bow of Rivet City (counts as stealing).
 * 2 are located next to a first aid box on a table, directly to the right of Vault 92's vault door.
 * 3 can usually be found in the Mechanist's Forge in the robot repair center.
 * 5 are located in Hubris Comics Printing on the lower level, 1st room on your right at the bottom of the southeast corner stairs.
 * 5 are located on a shelf facing the eastern wall in the lowest level of the National Guard Depot, next to some generators.
 * 2 can be found in a crate by Dr. Lesko's desk in the Marigold ant queen's chamber.
 * 2 can be found Next to the VAPL-84 power station in the truck guarded by 1 or 2 yao guai.
 * 1 can be found in the kitchen in Zane house in the Minefield.
 * 1 can be found in the yao guai tunnels, behind you on a shelf near where the scripted yao guai runs past.
 * 3 can be found on a table in Smith Casey's garage.
 * 3 can be found in Gallo's storage closet in the County sewer mainline after killing him and taking the key.
 * 3 at the store on Scavenger's bridge
 * A great number of fission batteries can be found in the Point Lookout expansion. They will often be found in places you might not expect, such as in suitcases or wardrobes.
 * Sold by merchants as a miscellaneous item.

Fallout: New Vegas

 * 31 In the basement of the REPCONN test site.
 * 9 spread over 3 floors in REPCONN headquarters.
 * 9 in Vault 11's living quarters and 2 in the lower level.
 * 9 in Vault 3's recreation area.
 * 2 in Zapp's Neon Signs.
 * 2 in Victor's shack.
 * 8 are for sale in Miguel's Pawn Shop.
 * 2 can be found in the The Gourmand kitchen where the bathrooms are; just past the bathrooms, there is a small supply cabinet. They are on the third shelf down, underneath a toolbox.
 * 1 can be found in Michael Angelo's workshop in the machinery shop where the lathe is, across from the fire hose box, on a metal shelf next to the toolbox.
 * Can be bought from Old Lady Gibson at the Gibson scrap yard.
 * A good amount (around 13) can be found in the Securitron de-construction plant in the Big MT in Old World Blues.
 * Inside Vault 22 in a storage room, along with various other items, such as scrap metal and wonderglue.
 * A few can be found at Cerulean Robotics in Freeside.
 * 1 can be found in the shack at Southern Nevada Wind Farm
 * 2 inside Harper's shack
 * 1 inside Lone Wolf Radio.

Fallout 3

 * Reilly's Rangers
 * A fission battery is required for fixing an access elevator during the quest, at the top of the Statesman Hotel. One can be found inside the hotel, but it is much easier to keep one extra in your inventory and bring it along for the quest.
 * A fission battery is used in the construction of the railway rifle.
 * A Spoonful of Whiskey
 * 6 fission batteries are required for the Point Lookout repeatable quest.

Fallout: New Vegas

 * Cass' moonshine
 * A fission battery is required to make Cass' moonshine.
 * Not Worth a Hill of Corn and Beans
 * Four fission batteries, along with many other supplies, are needed to repair a food processor.
 * My Kind of Town
 * Three fission batteries and 4 conductors can be used to reprogram Primm Slim to be the sheriff of Primm.
 * A fission battery, along with two pieces of scrap metal, are used to make Sierra Madre chips (listed as 'Sierra Madre Slugs' in-game) with the Coin Operator perk in the first add-on for Fallout: New Vegas, Dead Money.
 * Can be converted to energy cells in Honest Hearts, which can be in turn converted to other energy ammunition types.