Are you slightly mechanically inclined?
If so, you can try to parallel 2 batteries of the same voltage. Not sure what the flashpoints produce. But for example Ni-CD - Ni-MH AA are 1.2 v. If you parallel a good charged battery with a dead battery of the same size (positive - positive, negative-negative). Current from the one will flow into the other. From what I have read a fully discharged battery may form crystals between the cells. And doing this parallel for 20-30 second might clear the crystals (they will heat up and melt). With the shorts cleared, the batter pack might take a charge the normal way.