Battery Blowout

[Wired361]

I was charging my 7 cell GP3300 and i heard a hissing noise. I turned to look at my batteries and saw what looked like a plume of smoke coming out of a smoke bomb. I flipped an grabbed the truck and unplugged it and ran it outside of my garage and set it down. the battery continued to hiss and smoke. then it stopped and the next battery in series did it. This happend for all 7 batteries, it fried my chassis to the point where the batteries fell down out of the chassis, it is stock. All in all, i have 185 dollars to replace everything including chassis and batteries. Any ideas about why this happened and how i should spend the money?