[mike the snake]

If you run your Lipo down to 3 volts per cell you will ruin your battery in a hurry I think, as well as endangering you heli and the people around you!
3.6 volts is the safe cutoff voltage I THINK!
What I DO know is that the way to ruin lipos is to run them too far down, this is when they go out of balance, get really hot, and sometimes expand and explode.
I don't know the exact details, but what I do is NEVER fly tyhe heli past 80% of the battery capacity. I do this by timing my flights, and noting how much charge the battery takes in, so on my 2100 pack, if I charge it and it takes in 1700 or 1800 I know I flew for as long as I possibly could have, and I then know exactly how long i can safely fly.