I hope its the right translation, in german its Kraftstoffzelle.
You need at least 80 per Hero, to get them to gold. Sure Gold shouldnt be something you get in a day, but thats just to much. Why do we need this for every Hero? Why not anything else? There are so many items you can get and most of them you barely use. But this one you need for every hero, no matter if they are mech, energy or chem.