Working on our around a car battery can be dangerous if you are wearing any jewelry. Our own club member Jerry Sharp had an experience similar to the one below, except it was his watch band that burned him. This article was written by Mike Allen of Popular Mechanics. I picked it up from the Trail Birds news letter from SW Florida.
Let me relate something that happened to a friend of mine, a dentist by trade who likes to work on his sports car occasionally. In preparation for some other work, he elected to remove the battery from the car, using a box wrench to loosen the battery clamps. The wrench made contact with his wedding ring (he's left handed), and the ring in turn made contact with the battery hold down. A massive short circuit welded his ring to the hold down and to the wrench, which in turn was welded to the positive terminal. Car batteries store an enormous amount of energy, and they're optimized to deliver it in a very short period of time. A shorted car battery can easily deliver several hundred amps -- more than an arc-welding machine. Within a second, my friend's wedding ring was almost red-hot, and only a fast reaction with his other hand to break the connection by hitting the wrench prevented it from remaining connected long enough to melt. The ring had to be sawed off his finger at the emergency room, and it was more than a month before the burn specialist was sure he wouldn't lose the finger altogether. Two lessons here. First, remove all jewelry when working with tools, even something as simple as a box wrench. That's fairly obvious, eh? Second, always remove the battery's ground clamp before loosening the positive. If you remove the negative clamp and inadvertently complete a circuit to ground, there will be no current flow because the ground clamp is already grounded. Subsequent shorting of the positive terminal to ground will then produce no current flow because the current has no return path to the negative post. And, of course, always reconnect the ground last.
By Mike Allen Popular Mechanics
Take a very close look at the 6V battery in the photo above. Can you tell me what is wrong with it? firstname.lastname@example.org