One more thing to check is to see if one of the cells "vented". I built a 2000mah pack for my transmitter and cycled it twice prior to flying the first time. It almost cost me a plane as the voltage dropped form 10.8 down to 8.8 in a maner of minutes, less than five. I my instructor hadn't been with me, it would have been a dead plane because I can't hear the beeper frequency on the transmitter.

Inspect the pack closely and maybe carefully cut the shrink wrap off to get a better look. Look for gunk around th positive end of the batterys and also look for bad spot weld joints on the tabs.

Don