The only battery that ever caused a fire that I witnessed, was in the server room at a school I was working at as a campus tech. It was a huge APC UPS battery and there was smoke billowing out from under the server/switch room. I had to run in with the Science Teacher's fire gloves and yank the cord out of the wall while the maintenance guy used the fire extinguisher to put the fire out. We had a school full of junior high kids and it couldn't wait for the fire department. That thing melted all the cords that were plugged into it, and we lost 3 hub/switches that networked 10 classrooms. Scary.