LONG ANSWER. He hasn't been in combat mode too much (compared to canon) and hasn't had to go into full on Blade Mode at all. His fuel cells still have some good juice in them. Before the bombing if he ever felt like he needed to recharge, the Initiative took care of that for him (like after chasing down UE agents during the plague which involved him sprinting in ninja run).

Now, post-bombing, he is trying not to use up too much but of course we've had zombies, hunting down mutineers and now rebuilding so he IS draining his cells, just not as fast as he would be if he were chopping up Metal Gears. He'll have to find a way of keeping himself charged while here. Should be interesting! (If he has to go back to cannibalizing other machines, he will).

For his brain he gets nutrient gel packs from Tony Stark.