Why not just make it so the stacks don't deteriorate? Once you get a stack, you keep it, until you deactivate the toggle (or die). If you trigger a stack while they're full, you still get the energy from it, but imo that seems like the perfect way to make the power viable in a balanced way. You could go out and kill 4 trash mobs before doing a mission, and if you die, you're fucked. It would be a very high risk high reward toggle. Am I wrong?