I'm at level 16 and spoke with Sleem, just asked what he wants, hoping he mentions those electric chargers. It said it's already at 116/100%, and ready to follow my orders. Maybe it fed on the corpses of the slain snakes, I'm not complaining.
By the way my army is still Sea Dogs (they don't actually do anything, I wonder why I keep them around), Griffins (just got Time Back for level 1-3, they are finally useful), vampires, ancient vampires and 5 red dragons. I'm not a fan of sprites
I still haven't found Resurrect, but Sacrifice on vampires was good enough until now, and now with time back it's even easier.