[Al Skierkiewicz]

garyk,
the greater danger here is that if the two wrenches touch while both contacting battery terminals, the chance for welding currents to flow is very high. Once the wrenches weld together and to the battery terminals, they will go to several hundred degrees rather rapidly depending on the state of charge. That temperature is also reflected in the battery which causes a rapid pressure rise that can lead to case failure, electrolyte leakage and possible explosion. It is for this reason, all battery terminals must be insulated at all times. Only work on one terminal while the other is insulated. The voltage is low enough that it can't force enough current through your body to be felt unless it is across a very sensitive (read that packed with lot's of nerves) area that is wet like with sweat or salt water.