[MrForbes]

There is some danger with shorting the positive and negative power wires....lead acid batteries can explode if shorted. Also things get very hot very quickly when a battery is shorted, you could get burned trying to disconnect the battery (I saw this happen at the first regional I attended, a team had a demonstration device with a motor connected to a battery, the wires shorted and started smoking, and a student burned his hand attempting to disconnect the battery cable)