Fusion core (Fallout 4)

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

Gameplay
Fusion cores are used to power and activate suits of power armor. Each core provides roughly 20 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 jet pack modules causes the power to drain much faster, whereas walking consumes less power and remaining stationary drains none. While the Sole Survivor can utilize power armor without a fusion core, they will be unable to move at a pace greater than a slow walk (similar to being overencumbered) and actions requiring AP will be restricted.

Fusion core lifespan is represented as a percentage. 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. Instead of increasing the maximum charge percentage, these will slow the rate at which the charge level drains.

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

Fusion cores glow when they suffer critical damage and eventually erupt in a small but powerful nuclear detonation.

The core of a worn suit of power armor may be targeted using V.A.T.S. A successful hit will cause the core to suffer critical damage, causing a small nuclear explosion behind them, forcing the character wearing the power armor to exit it.

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.

Weapons using this ammunition

 * Gatling laser
 * Final Judgment
 * Aeternus

Locations

 * Sentry Bots carry two 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 power armor such as Brotherhood of Steel members and Atom Cats. Successfully pickpocketing it will force its user to exit the power armor.

Behind the scenes
In previous installments of the Fallout franchise, power armor was 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.

Bugs

 * 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.
 * 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 the said weapon. Solution: Unequip and re-equip the weapon.
 * 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.
 * It is possible to acquire an infinite supply of fusion cores on the main deck of the Prydwen by stealing them from NPCs walking around in power armor. After stealing the fusion core from NPCs, they will exit the power armor and enter it again, which will spawn another fusion core in the NPC's inventory. This exploit can be repeated indefinitely; the only thing that can break it is saving and loading, which will cause a duplication glitch that spawns another empty power armor, and the NPC in the original suit will not be able to move. Leaving the area for some time and returning back may fix the glitched NPC and remove the duplicated power armor.