Well, the real reason that the items take up battery is because we didn't want people spamming the "drop spring" button since springs kill on impact. We decided against using individual ammo indicators for each item since we wanted it to be a more streamlined, arcadey experience. But if it helps, just imagine that when you are spawning a spring or a girder the ship is fabricating them with an advanced 3d printer that takes up a lot of energy.