1. take one vapex battery
2. remove cellophane wrapper.
3. use in car for a few races
4. have a heavy crash and roll car over
5. stand back and watch the flames

the plastic seal at one end has the wires next to each other.  As the car 
twists and turns the seal actually bites into the insulation.  The car is 
really designed to take home made batteries where as the vapex has them in a 
traditional tamiya style stick.  car rolls, stick comes out of car, stick 
twists so that base of wires (now stripped) touch each other.  Other end of 
battery with the big bar across the contacts heats up and melts outer case 
of battery, car and racing carpet also catches.