One strand from a length of hook-up flex will draw no more than a 21 watt 12v globe, so you obviously don't know what you are talking about.
One strand is exactly the same gauge as a 3 amp fuse.
You never did mention one strand did you? If the battery is releasing gas for some reason, a large spark could cause a serious problem. I think this is foolhardy advice.
You need to be specific then colin, cause if you tell someone to just use a piece of wire to short out a battery and they happen to use a short piece of heavy wire it wouldn't turn out so well.