You can't overdischarge lipo - running them below ~3v/cell can cause damage (swelling). You need some kind of warning. There's an audible alarm with a flashing light that generates various combos of alarm and light based on what batt voltage. You need something like that or maybe just a timed flight so it's short enough to keep your lipos from overdischarging.

Its not a good idea to just run them as low as you want to and depend on immediate recharging to keep them from swelling. Dropping below ~3v/cell will cause damage, if it doesn't swell, cycle life will be reduced.