Anything less than 3.7 volts per cell is BAD! If your total voltage at the discharge plug 8.9 vdc, I would have to agree with BH in that the pack is dead!

The #1 key thing to remember with Lipo's is not to over-drain them, they do not respond like the Nicads or NiMH batteries which allow them to be drained to almost 1.2 vdc per cell.
Excessive current draw can cause them to swell, reducing there ability to hold/take a charge. So if your motor draws 25 amps under full-load, use at least a 15c (30amp max draw) lipo although a 20c (40amp max draw) would be better.
A battery monitor is a good investment (about 25 bucks), I use the HR Poly X lipo monitor on 3 of 5 heli's I own, it warns me of when I'm approching the bottom of the battery (with both visual & audible indicators), has an adjustable range and works with up to a 4 cell Lipo.

Shadow