Strangly enough that power construt could have uses with a few mods. Each charge would last only 1 phase and after that you would lose the +50 stun. For that one phase you would be up, but after that you would likely go back down below 1 stun, until 3 more phases past, since you would be out of charges. Likely you would try to recovery during the first use of the charge, so you wouldn't have to use the other charges or you just leave it as a "last great stand before your knocked out" kind of thing. Of course it can be an abuse, so I'd likely not allow a PC to have it, but something like it with a single charge could be interesting for a villian to have.
As to End Reserves on Charges, I'd likely have to see the actual construct.. I'm think it would be unlikely that I'd find one I'd allow. Still I think Steve's comment was more along the lines of "I'm not forbiding since there might be a cool effect only possible by allowing it".