This is a true story (you can't make things up like this):
My buddy gets an XS-1 Yamaha. On his very 1st ride after sorta restoring it all winter, he didn't have a battery, so he bungied a HUGE ST1300 battery to the seat, rigged jumper wires, took it for a ride and as he rode down the block, the wires melted, started smoking and lit his pants on fire. I watched it ALL happen (priceless). Thank goodness we had plenty of beer (before and after) to quelch the flames.