Fuel cells do not consume fuel. It converts hydrogen and oxygen into water. You can reconvert water back into hydrogen and oxygen. You can conceive of a fully c

Fuel cells do not consume fuel. It converts hydrogen and oxygen into water. You can reconvert water back into hydrogen and oxygen. You can conceive of a fully closed-cycle system for this. But it's not worth it, since you are just carrying a big tank of water for no reason. It is a smarter solution that a battery which does carry everything at all times.