Battery
Carried charge: fill it at a base, empty it into a ship. How much it holds comes from the ore it was wound with.
A battery is for moving current about, so what it's made of decides how much it takes: 380, plus 3.2 for every point of the ingot's Reactivity.
Seat it in a Battery Dock to fill it from the grid or empty it into a ship. Any generator also charges a battery sitting in its cradle.