I was evaluating a new device in an industrial environment. To test it, I had a shop-made electronic test device which used a simple little alkaline 9V battery (size 522) for power. Because I didn't want to have to terminate my testing if the battery in the test device ran low, I carried a spare battery in my pocket.
The morning wore on, and I was busy taking data. My hand brushed the pocket that held the battery, and, to my surprise, it was hot! I reached in my pocket and yanked out the spare battery -- it burned my fingers! I threw the battery down on the grating and wondered what the heck had caused all that heat.
Looking at the terminals on the battery, I noticed two discolored spots on the brass. I also emptied my pocket and found a very warm quarter. Ah, ha, said I to myself -- the quarter must have worked its way across the battery terminals, causing a short which caused the internal heating of the battery. I gingerly picked up the now somewhat-cool battery, placed the quarter across the terminals, and the battery very rapidly started to heat up again.
Lesson learned: Even small batteries have the potential to heat up considerably when abused. I never carried a spare battery in a pocket with anything else metallic in it again. Now when I dispose of any battery, I always wrap it in tape so the chances of it shorting to something else are pretty much nonexistent.
This entry was submitted by Bob Groh and edited by Rob Spiegel.
Bob Groh worked for more than 40 years as an electronics design engineer, mainly in radio and communications design, with a few excursions into management, and even one stint working for an A&E firm.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
I recall reading about police officers cooking-off pistol rounds by sticking spare bullets into a back trouser pocket and then dropping a handy-talkie into the same pocket. The charging studs on the bottom of the radio would be shorted by the bullets and the heat generated by the short-circuit would cause them to detonate. NiCd cells pack quite a wallop when shorted and could even potentially explode. AA NiCds can easily drive several amperes into a short circuit. Any batteries, primary or rechargeable, are potent energy sources and should be treated with respect.
As a mechanical engineer, I have to admit that this is news to me. I don't remember being tempted to do the tongue test while in school. And I never knew a 9V could pack that kind of wallop.
This tale is no surprise to those of us who as budding young engineers learned that the easiest way to test 9V batteries -- at the time, the preferred power source for transistor radios -- was to touch one's tongue to the two terminals simultaneously. The 9V is made for this, as the terminals are side by side. (You can't do it with AAs, Cs, and Ds, where the terminals are on opposite ends of the battery.) So if you got a big sting, the 9V is good. The hit diminishes according to how run down the battery is; a spent battery has no wallop. When I say "hit," I should add there's nothing relaxing about it. You get a good shock. Supposedly this is a dangerous test to do, because if your skin resistance is low enough, you can die. Never heard of anyone dying from this, though.
As an adult, since transistor radios are no longer so popular, and the ones that are around use AAs, the 9V tongue test is applicable to smoke detectors. In testing them, I've come to the conclusion that the "change the battery once a year" thing, which has become common practice, is more a marketing ploy to sell more batteries than a necessity. When I am (forced to) change those batteries every year, they're still good. I'd keep 'em, but there's no use for them anywhere else.
It's most likely to happen with a 9-volt battery, Beth. The terminals are right next to each other. I'm not going discount the chances of it happening with a cylindrical battery, but I think you're ok with your regular junk transportation. Maybe skip the aluminum foil, but otherwise, ok.
Wow, I did the exact same thing when I was a teenager. I bought a 9V battery at the store and just dropped it in my pocket. It shorted across a coin and got REALLY hot in my pocket.
Those little 9v batteries have always packed a real punch. Since the negative and positive terminals are right next to each other, you can put your tongue on the two terminals to see how much juice is left. The new ones are quite a shock.
Little batteries, even well-used, can pack a LOT of enegy! I've had a very similar experience with 9V batteries, which are more prone than most common types to accidental shorts like the one described because of the terminal orientation. AA cells could be even more dangerous if shorted, but the likelihood of something conductive contacting both terminals is much lower.
I use dry batteries to power some antique (tube) radios and have developed a very high respect for their power capability.
Beth, I think a spent battery is less of a problem than a fully charged one, but it certainly makes sense to remember that all batteries are actually power sources. Consider that model rockets are ignited with only a 6v lantern battery.
Now that's a lesson learned that everyone can benefit from. I can't tell you how often I pick up random things left lying around the house--nails, batteries, toy parts, change--and dump them in my pockets with the intention of disposing of them at a later date. I won't be so quick to load up my pockets with random, spent batteries any more after hearing this Sherlock Ohms tale.
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