I agree with most of what nol5000 says (maybe not the 7 part…) but the problem isn’t with the players being too anxious to play the game, its just that they need a way to get more without having to pay or fill out infuriating surveys. I agree with most people that the limit should go down from 1 energy in ten minutes, even if not all the way down to 5.
However, nol5000, you are definitely right about heat: That doesn’t need fixing nor major adjustment. Exp would take this wonderfully simple but effective system and make it over complicated and too annoying to use.
One more thing: The fun won’t magically “Run out” if you play this 8 hours per day. My little brother can spend 24 hours a day on Call of Duty and will still never tire it out….