That's why I recommend people use the 12v black and decker because it tapers off the current once it gets close to fully charged so you don't get the voltage spike. I don't have that charger so I don't know what it's like but a friend of mine who has it says it almost destroyed his batteries too and he caught it just in time. It sounds like that charger doesn't taper off the current.

When you charged all the batteries, do you know what the total overall charge was? I think the highest I've ever had mine up to was about 42.99v on the 12 cells. I think the highest they say you can take it is up to about 43.7v.