A cutoff time is preferred!! It is okay to drain it down till it starts to slow down significantly, but it does risk a chance or damaging your cells especially if you do it more than FIVE Times. This typically is the limit for most lipo's depending on maH!! Run your battery one time using a timer and time till it starts to slow down. Then just make a timer on your radio or stopwatch to go off at least 3-5 minutes before it started to loose its power to ensure that to much power has been drained from the pack.