That would make sense. The game does gloss over recharging to some extent, so what would probably be easiest is something closer to a hybrid of the psionics system(power points) along with an overheating system(so recharge, but you can fire pre recharge. Its a good way to damage your suit, but sometimes its worth it).

Of course, this assumes your sticking to D20 entirely. If your still up for a system switch, I would throw in Fudge again. I've recently used it for a game involving powered armor (its intentionally ridiculous, basically the technologically advanced humans and the magic using demons are both at war, with limited strikes towards humans from the demons. In addition both of them are seeking El-Dorado and Atlantis, believed to be super weapons with tons of magical energy. The vast majority of humans are not aware of the war, as it is underground. Some of the people actually fighting the demons have powered armor, and Fudge worked beautifully for it.)