I think a better idea would be see what the run time is for that battery in that system. The reason I say this is: Nicads and LiPo's pretty much output a steady voltage and current up until the very last. Then it drops off sharply. I'd figure my run time and give it a 25% safety window. 4 hours run time, fly for 3 hours... or whatever.

The loaded voltmeter is a quick check, it won't predict 5 minutes from now.