Alien Power Cell (Fallout 3)

The alien power cell is an energy weapons ammunition of alien origin found in Fallout 3.

Characteristics
This alien ammunition type is used with only two weapons: The alien blaster, and the unique variant, the Firelance. Represented in groups from 11-25 by a small cylindrical battery-like object, alien power cells are light blue and luminescent, easily identifiable from other ammunition types and the generally bleak setting of Fallout 3.

Used in

 * Alien blaster
 * Firelance

Locations
A maximum of 1152 alien power cells can be found in all expansions, without glitches. In addition to the static locations, in the Mothership Zeta add-on, a character may find even more power cells on dead aliens, guardian drones, and support drones.

Base game
A maximum of 362 alien power cells can be found in the core game.
 * 24 can be found together with the Firelance in the random encounter "Unidentified Flying Debris".
 * 120 (10 stacks of 12 cells) can be found in and around the alien crash site.
 * 96 (8 stacks of 12 cells) can be found under an overturned truck in a radioactive crater due east of Fort Bannister. Upon seeing bombed out buildings, changing heading a little to the north will lead right into it. There may be some Enclave at the site and an Enclave scientist at the truck checking it out (Note: This location only deals minor radiation, approximately 1 Rad/sec).
 * 2-22 without the Scrounger perk (17 on average), or 2-122 with the perk (92 on average), can be found in two ammunition boxes in Fort Independence, in the Outcast weapons room (hard locked door) containing the Miss Launcher. The method by which the outcome is determined (rolling for 1s at a 75% chance, 10 and/or 50 times) pretty much guarantees that the results will be on the high side (i.e., near 75% of 10 or 50).

Broken Steel add on
A maximum of 425 more can be found in Broken Steel.
 * In Broken Steel during the Shock Value quest, they can be found in two separate locations within Olney Powerworks. In the room with the automated turrets and walls of computers, just above the turrets there are two ammunition boxes each with an average of 40 to 45 (Scrounger-affected esteem). Near the Tesla coil, in the room at the bottom of the coil's pit, there are 36 (3x12) power cells on the stove and table.
 * A nice amount can be found in the Armory of the Mobile Enclave Crawler at Adams Air Force Base along with an alien blaster: from 9 to 12 are inside the alien blaster case in the armory (this particular stash is NOT affected by the Scrounger perk). Plus, the 3 average-locked ammunition boxes just below the blaster's contain an average of 46 cells each, pretty much like the containers in Fort Independence's storage room, assuming that the Scrounger perk is active; otherwise, they will not contain more than 30-36.
 * Destroying the Citadel during the "Who Dares Wins" quest makes 72 (6 clips of 12) show up in the armory in a room with mini nukes and Tesla cannons.

Mothership Zeta add on
There are approximately 365 alien power cells on Mothership Zeta.
 * 48 (4 x 12) on the back shelf of the room where the Lone Wanderer reunites with Sally after being guided through the Steamworks; there is also a healing archway and two containers in the same room.
 * 44 (1 x 20, 2 x 12) in the robot assembly area, downstairs in the first chamber, on a corner shelf near a teleporter room, near a small container, opposite the robot escalator. There are another 24 (2 x 12) that clip into the wall, only obtainable via console commands.
 * 26 (1 x 15, 1 x 11) in a box with a Nuka-Cola Quantum on the second floor of the engineering core where Sally and the other non-player characters are located. It will only appear after the third generator from the quest Among the Stars is destroyed. The box is located on a railing behind the workbench; accessing it requires either jumping or pulling it over from the side.
 * 51 (3 x 12, 1 x 15) in the weapons lab area, on the shelves next to the atomic pulverizer.
 * 87 (6 x 12, 1 x 15) on a set of tables towards the end of the weapons lab area near where the Destabilizer is found, along with a cache of weapons and armor, including the Gatling laser, plasma mines, and Tesla armor.
 * 109 (7 x 12, 1 x 25) in the biological research area on a set of shelves under a catwalk, where the Lone Wanderer reunites with Sally and the others.

Tips for locating

 * Alien power cells glow in the dark, which can be useful for finding them, since they are small and hard to spot.
 * Another way to find them is to order Dogmeat to search for ammunition when the cells are nearby.