Ok, thanks, I'll disassemble it and see.Not good news. Depending on the chemistry it shouldn't be lower than about double that. At 20V it's telling you that most of the cells are way below their spec'd minimum voltage or that one or more cells are dead. Low cell voltage can lead to early cell, and therefore, battery failure. Can't really say if that's all ready happened or not. You could take the pack apart and check individual cell voltages. If none are dead and you're willing to spend a few $ on the charger you can test the pack by charging it up. If the voltage comes up, you're good to go. Otherwise you've got a new charger and a dead battery.