Lipo wouldn't take a charge.

[ilpufxit]

I thought I killed my lipo but it looks ok. I'm running a Maxamps 4000mah 5s pack in my 8ight with a Quark 80b and 1512 2.5d/f. I ran it till the body cracked at both posts, worked awesome, had a great time. Anyway, when I charged the battery with my Hyperion charger, it charged at .4 amps for a couple of minutes and then started beeping and flashing "check battery, low voltage". When I first connected it to the charger, the pack was at 16.49v. I tried re starting the charger a couple times, it kept limiting the charge to .4 amps (normally it charges at 2.9 amps) and the voltage slowly climbed to 18V. As soon as it hit 18V, the charger switched to 2.9 amps and everything was normal. So, what gives, the pack should go down to 15V right? Do I need to program volts per cell into the charger? Any help would be appreciated, I'd really hate to kill my pack.