Generator

Generators are devices that use a series of physical and chemical changes to make energy. They were used by both UNSC and the Covenant.

Covenant
Covenant generators expand upon a single Plasma Battery to multiply its yield, which is transferred and stored in Covenant barrels that are attached to the base. These barrels have seen unattached to the generating bases which are probably transported and used to fuel Covenant vehicles. These generators can be found on Burial Mounds and on Metropolis, near the Marine command post.

The armor plating on these devices prevent tampering or destruction by the player on Campaign mode. It is likely that the fuel that the device generates into the detachable and replaceable tops might be plasma-based. This means that they could be used to fuel the systems on Covenant Vehicles, such as their weapons, fuel, etc.

UNSC
UNSC generators are used to create electricity. These generators are also a Forge item in Halo 3. They can be placed in certain maps, such as The Pit, and Orbital.