Originally Posted by Duster_360

Check the voltage with a dvm - how low is the lipo reading? Why is it low - did you overdischarge it? Hyperion charger is expecting something over 6 volts for a 2S lipo (min 3volts/cell) so if its below 6, charger won't charge it. From the charger's prespective, this is a potential safety issue.

If you simply overdischarged it and its in good shape (not puffed), you can try to charge it as a 6 cell NiMH at 0.5 - 1amp ONLY until voltage is back up over at least 6volts, say 6.1 or 6.2volts. As soon as voltage is up, stop the NiMH charge and then charge it as a lipo - it should now charge normally.

Watch it as it charges to be sure it doesn't start to puff. If it charges ok and runs ok, it will prob be ok. If it puffs at anytime during this, its time for a new lipo as this one has become unsafe.