THUNDERCATS! (Su): Your body becomes a big electrical sponge. If you are Psionic, you convert Electrical damage into temporary power points. If not spent within 24 hours they dissipate. If you cast spells, Electrical damage you take is converted into spell points (see Unearthed Arcana pages 153-157). You may substitute use these points to cast additional spells per day, but the points fade within 24 hours if not used. You may not hit yourself with Electricity to gain power in this manner.
Seems quite a bit abuse-able, but there are official ways of doing it better, so nothing to complain about. I's it 1:1, because that's a bit much.
The grenade effect wasn't exactly what I was thinking of, but is still good.