Although the energy thing is annoying at times, it's not like there's nothing else to do. Go battle in the arena, reorganize decks, check out the factions, buy new cards, w\e you want to do. It's not a game killer, it just forces you to get out of the solo player mode for a bit.
Awesome game. Concept is nanowars, but most games aren't TRULY original nowadays. Excellent derivative.
Quake = game over.... 57 battles. Could be a lot less