[gepetto]

So your point is that the number of attacks you get for credits from a 20$ donation at any level should be the same?

Makes sense. One way to do this is to make the number of credits required for an energy refill depend on the number of attacks you do with a full energy bar.

Don't forget that the other thing you do with energy that you get from refills is training. So the number of attacks and the training has to be balanced somehow. You can prob do that by eliminating the posibility to top-up happiness... or at least make it more expensive.