Power core

Power Cores are Forerunner devices presumably used to store plasma energy to power up Forerunner machines. They are recognized by their low pulsating humming, and can be found mounted on walls on some Forerunner installations. An explosion of a Power Core can be lethal at close range. There are similar, although larger devices called Energy Cores.

Gameplay
Power cores can be seen in Halo 2 and Halo 3, in Campaign and Multiplayer levels. They can be used to kill anyone who passes by if they are shot at. However, it takes two Power cores explosions combined to kill somebody with shields. In Halo 3, certain maps can spawn the Power Core in Forge.

Trivia

 * When two power cores explode in Halo 2, one will throw the other into the air where it explodes much like a Fusion Core, but in Halo 3 they both explode simultaneously like a Plasma Battery.
 * The Power Core is one of the least seen explosive objects in the Halo series in Campaign.
 * They may be created from mines such as the Gas Mine in Halo 2, as that facility produced many similar power units, such as Gas Containers.
 * It is comparable that the Power Core is the Forerunner surrogate and equivalent for the Covenant Plasma Battery and the UNSC Fusion Coil.