I think that overall PA should be much more rare than shown in the FO games. Originally, pre-Apocalypse, it was pretty much 100% US Military. And probably no more common (given the cost per unit being a BIG drain on the Pentagon's budget) than, say, F-22s are today. (That is, @200 in 2015.) Even multiplying that by 100, the total would be scattered all across the country. Deducting attrition from the fighting in Alaska and the outright destruction of most of them when the military bases they were located at got nuked on A-Day, followed by the attrition over 200 years of being shredded by Deathclaws and blasted by mininukes, there really should be very few left in the world. But here we have every Paladin in the BoS in all its many chapters being fully armored with complete sets of T-51b. Plus all the sets found in FO, FO2, FO3, FONV, and now FO4. Bethesda seems to think that the US Military cranked out those VERY expensive suits like VW cranked out Bugs in its heyday.
As for the powering system, having some kind of limited power source is, I think, a step in the right direction. But a power supply that can be entirely depleted in the course of ONE prolonged battle? There's no way that the Pentagon would approve of that particular MilSpec. Maybe as little as a 72-hour to be depleted, provided it was rechargeable. Otherwise the Pentagon would be looking at billions/trillions of dollars of military hardware being made useless just because it ran out of million-dollar "batteries". That would be like having entire Armored divisions frozen in place because they ran out of gas. (Where's the Red Ball Express when you need it?)