Powercells store massive amounts of power. They can be placed either individually, or they can be placed next to one another to form a multiblock structure. Powercells will automatically distribute RF between themselves and their neighbors, and will join up into a multiblock regardless of tier.
Powercells have no UI, but can be configured to input, output, or ignore power by hitting the desired side with a smart wrench in Wrench Mode. Blue is input, Yellow is output, and a blank side is neither.
By default, the Powercell (low) can hold 500,000RF each.
By default, the Powercell (Medium) can hold 4,000,000RF each.
By default, the Powercell (high) can hold 20,000,000RF each. That's a lot of RF!