How to get more Energy Cubes?

Been trying to get more so I can finally unlock the Surgeon so I can finally get past the tier I'm stuck on (can't get a robot chicken), but for the life of me I can't figure out how save for beating up the protector. Which is more or less impossible for me right now since he's way past a manageable health limit. Last I checked he's at 3 million. Plus, my luck with the chests is never all that good.

Any ideas? Help please?