Fusion core (Fallout 4)

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The fusion core is a type of ammunition in Fallout 4.

Characteristics

Fusion cores are used to power and activate suits of power armor. Each core provides roughly twenty minutes real time (or approximately 10 hours game time) of power armor use when jogging (default pace). Actions based on Action Points (AP) usage, such as holding breath when using scoped weapons, sprinting, utilizing V.A.T.S., or Jetpack modules causes the power to drain much faster, whereas walking consumes less power and remaining stationary drains none. Fusion cores have a total charge of 100.

Fusion core lifespan can be extended by 10% by collecting the Repair bobblehead, and by up to 100% by investing points in the Nuclear Physicist perk.

The Gatling laser utilizes fusion cores as its ammunition, each core providing 500 shots. Nuclear Physicist can increase the amount of shots per core up to 1000, but the magazine capacity will remain at 500. Also combining with Repair bobblehead, the total amount of shots can be raised to 1100.

Fusion cores can also be ejected from power armor suits if one has the highest level Nuclear Physicist perk and no other explosive devices are currently equipped. Ejected cores land a short distance behind the user where they act as a sort of timed mine with a destructive force similar to that of a Fat Man's projectile. Note that contrary to the perk description, the cores cannot be actually thrown like regular grenades.

In addition to fixed locations below, fusion cores may also spawn in groups of four in certain ammo boxes across the Commonwealth. Cores can also be spawned in other container types by means of an eyebot pod, but only one at a time.

Locations

Location	Amount	Description
ArcJet Systems	1	In the room where the Sole Survivor can restore power to the elevators
Atlantic Offices in the Glowing Sea	1	Atop the roof
Boston Airport	1	Spawns in the cargo area after Reunions
Boston mayoral shelter	1	In a room off the basketball court with a sign above it that reads "Restricted Area"
Cambridge Polymer Labs	1	One can be found in the office, either by picking the master lock or successfully finishing the laboratory's research
The Castle's armory	5	Including from Sarge sentry
Concord Civic Access	1	In a dark corner opposite the small drug cache that the mirelurk guards
Crashed boat	1	Southwest of the Harbor Grand Hotel on the shoreline there will be a crashed ship with containers arranged to the side of the boat with flames trailing behind it. On the bottom floor there will be a Fusion generator with the fusion core
Erin Combes	1	Might give one for finding Ashes in the quest Here Kitty, Kitty
Four Leaf fishpacking plant	3	Two inside (one of them behind a mag-lock door) and one on the roof of the building
Goodneighbor	2	On a shelf inside the train cart strongroom in during the quest The Big Dig
Greenetech Genetics	3	On the top floor, two behind a security door locked at master level, and one behind a door further on locked at advanced level
Gunners plaza	3	2-3 behind a novice locked door in a room on the opposite side of the elevator on the roof. One other one can be found on the center of the roof behind a door with a generator, running the fusion core
Near Jamaica Plain	1	On the floor in a house on the outskirts of Jamaica Plain, on the floor next to a dead feral ghoul
Kendall Hospital	1	In the basement
Longneck Lukowski's Cannery	1	In the basement area after the sewer section; be careful of mines
Malden Center	3	All near the generator after descending in the elevator. One is one the ground in front of the generator. The other is in the cardboard box on the table to the left
Malden drainage	1	At the end of the canal just north of the Taffington boathouse
Milton parking garage	4	A part of one possible reward for completing the trap-ridden maze inside the parking garage
Mass Fusion containment shed	1	Behind a mag-locked door (unlocked via terminal right above it). The area is heavily irradiated
Medford Memorial Hospital	1	West on the second floor in a generator room.
Fallout 4 merchants	1	Any merchant who stocks ammo will most likely carry up to 5 at 100% charge, and may carry one or two others at lesser charge (usually 40%-90%)
Mole rat den	1	In a room to the right of the center room in the den
Museum of Freedom	1	Lowest floor behind a security door (Novice terminal). Sturges asks the player character to retrieve it during When Freedom Calls
Mystic Pines	1	In the basement. The door to the basement is locked (Advanced) and requires 1 point in the Locksmith perk to pick
Poseidon Reservoir	1	On the main road at a military checkpoint north of the reservoir, in a power armor
The Prydwen's maintenance bay	2	Can be stolen off suits on The Prydwen by sneaking behind them (Paladin Danse will disapprove)
Quincy church	1
Railroad HQ escape tunnel	1	Near the exit behind a security gate that can be opened from the Expert terminal to the left of the door
Recon Bunker Theta	1	Can be found during The Lost Patrol
Red Rocket truck stop	1	Mole rat den
Revere Beach station	1	Obtained for returning an Overdue book at the arcade building near the the station for fifty tokens
Roadside Pines motel	1	Behind the motel on the west side of the building.
Robert Joseph MacCready	1	As an active companion, he will frequently provide fusion cores in lieu of ammunition if he is equipped with a set of Power armor.
Robotics disposal ground	3	In chest near the robot in the center of the room. Two more can be retrieved from the robot by enabling it and then self-destructing it
South Boston military checkpoint	1	In a power relay under the elevated freeway just east of the checkpoint
Starlight Drive In	1	In the building behind the screen, with a locked (Novice) door.
Suffolk County charter school	1	In a generator in the basement
Super Duper Mart	1	In the generator room in the back
The Switchboard	1	The fusion core is best accessible from the escape tunnel
USAF Satellite Station Olivia	1	In the main center room in with the generator and the catwalk. Generator emits a buzzing sound.
Vitale pumphouse	1	In the second room, requires combination "10-4-5-1" to access.
Walden Pond gift shop	2	In a suitcase during the mission where one fights a group of raiders to liberate a village
Waystation	1	When following Dogmeat during the Reunions quest
Weston water treatment plant	1	In the eastern hut
Wilson Atomatoys factory	1	Southern side
Wreck of the FMS Northern Star	1	Inside a generator on the ground level, near the bow of the ship
Yangtze	1	Inside an open footlocker in the crew quarters
The Nucleus	2	On the metal shelves in the first wooden shack after the Decontamination Arches
Glowing Grove	1	On one of the tables

Sentry bots carry 2 or more fully charged fusion cores that can be recovered after the robot has been destroyed.
It is possible to pickpocket fusion cores from characters equipped with a power armor such as Brotherhood of Steel members and Atom Cats.

Notes

The item's value is independent of its charge level, however drained cores are discarded and cannot be sold. This is a helpful way of gaining caps if remembering to transfer cores before they are discarded. The player character can use a fusion core almost completely (even so the charge reads 0/100), and sell it for roughly 120-160 caps as long as it is still in their inventory.
Contrary to how it was advertised prior to game launch, fusion cores are not exactly rare, as most shop keepers and trade caravan owners will have at least one or two cores for sale, and they can also be found along with other types of ammo as loot in containers.
While in power armor, besides the current fusion power level, the players can see how many fusion cores are available in their inventory. If 100 or more cores are available, the counter will top out at 99 as it only has two digits.
A suit of power armor doesn't need a fusion core in it for a companion to enter it. If a fusion core happens to be in a companion's power armor, it does not drain from use.
Fast Traveling does not drain energy from fusion cores while wearing power armor.
Using the jet pack drains the core's power much faster than any other type of armor operation.
Since fusion cores are used as ammunition for the Gatling laser the scrounger perk allows to find them at an increased rate.^{[verification overdue]}
Fusion cores glow when they suffer critical damage and eventually erupt in a small, but powerful nuclear detonation.
Leaving a fusion core in a power armor parked in a settlement will very often result in a settler, companion or even an invader wearing the power armor. And while the core will not drain, there may be some very undesired consequences. Such as, power armor being destroyed in combat, named settlers not having a dialogue option to ask them to exit the armor and therefore making it not usable by the player, or the power armor being discarded somewhere in a large settlement making it hard to locate.
Fusion cores at different charge levels do not stack together.
Fusion cores have the same hit chance as the NPC's torso in V.A.T.S. (assuming player is at the backside of them).

Behind the scenes

The following is based on unverified behind the scenes information and may be inaccurate.

The fusion core is most likely powered by nuclear fusion. This possibility is strengthened by the fact that the Fallout universes machines are almost exclusively powered by either solar or nuclear energy.
In previous installments in the Fallout universe, power armor is said to be powered by a TX-28 microfusion pack that can power the suit for over a century. It is never explained why a brand-new pack can be exhausted within 24 hours.

End of information based on unverified behind the scenes information

Bugs

PC Sometimes, putting a fusion core into the armor may send both the fusion core or armor straight down, through the floor. Reloading a previous save is the only known fix. ^[verified]
Playstation 4 Completely draining a fusion core while in power armor and having a weapon not be fully loaded at the time may cause the game to show that the player character has no ammo for said weapon. Solution: Unequip and re-equip the weapon.^[verified]
Playstation 4 Having multiple fusion cores at the same level the power armor had when the Sole Survivor stepped into it may result in them all draining with the one in the power armor.^[verified]