You don't so much "check them" as fly them a couple of times and get an average consumption per flight. Then figure out a safe number of flights with a safety margin and charge after that number of flights.

With my 50cc stuff I charge and fly 4 flights. Thats 6 big servos and an ignition. I get 4 flights and put 60 percent of the capacity back in.

No regulators, no self discharge, no downside.