The worst i ever did was have a short between 2 cells. I had tweezers fall across, well one cell burnt, yet the other was fine. I still have the tweezers, but man, they were glowing orange, and they even were flaming
I only know of one battery pack actually expiring while i was there, the battery shorted on someones chassis, and was smoking down the back stretch. Great show, but did damage to the car.