Normally the minimum voltage values for LiPo's are fixed on computer controlled chargers.

The reason I thought to ask all of this, is that I had a similiar problem with a pack on a Team Checkpoint charger.

The TC 1040 charger would not charge the pack, so I placed the pack on a "dumb" charger for 20 minutes, and found that I could charge the pack again.

Normally an overdischarged LiPo pack is considered to be damaged beyond repair, so this is a safety feature.

Try to adjust your ESC programming to get it to determine the correct Cutoff voltage.

If you are unable to do this, I would suggest running the plane for 1/2 the amount of time you did before ( ALWAYS USE A TIMER!!!! )....

Then take the pack and charge it noting the amount of charge put back.

Let's say the pack is rated for 1800mAh

You take it out and fly it for 8 minutess. Then you charge tha pack and find that the charger put back 900mA of current.

An 1800mAh should only be let to discharge to around 1650mA, so you know that the MOST you want to fly will be about 14 minutes.

Set your flight timer for 13 minutes, leaving you with a 1 minute safety margin for missed approaches.