Hi!
I've been playing single player (campaign).
Although I have 20 energy regeneration points per turn, my energy bar was full after every turn, no matter how many energy points I've spent.
In every turn I've used drone Blue snow which spends 9 energy per use, side weapon Le Gun which spends 8 energy per use and Mach 2 Cannon which spends 14 energy per use.
I saw this happened, but I was not sure, so I've watched my energy bar throughout entire next single player battle and this occurred all the time.
Probably happened before, but I didn't pay attention.