Added by the AvP : Humans module is the Battery. Batteries are vital for long term storage of FE and power in general. At max, a battery can hold 1.5M FE.
Additionally, it can be upgraded using specific upgrades to increase transfer rate, hardness and overall storage of FE.

(Visual Display.)
Battery Recipe.

Steel Ingot. - Steel Ingot. - Steel Ingot.
Lithium Block. - Neodymium Magnet. - Lithium Block.
Aluminium Ingot. - Machine Block. - Aluminium Ingot.