I have noticed you get extra energy from Expose Armor. I have 2/2 Imp EA and it only costs 15 energy. Combined with overkill it only costs 5 energy, while relentless strikes restores 25. That is a 10-20 energy gain, like an extra renatakis. Also if your EA is missed/dodged/whatever you will gain 20 energy from quick recovery giving you 5 extra energy.