Energy overflow
Lets say your on a map that costs 3 per tile. You get to the end of your energy and have 2 left. You want to keep going so you use a refill. It brings you back to full energy but really you just wasted 2 energy. I think it would be a good idea for that extra energy to carry over so when you use your refill it would bring you to 72. 70 from the refill and the 2 from what you had left over.