@cvandewater- Point well taken; even if you blasted your tongue to bits (not possible as you stated), it would sure be life-changing but not life-threatening ! The TSA/FAA loose battery concern is an item shorting and getting hot, the topic of the article. Higher energy density means a bigger possibility of starting a fire. Not a function of chemistry, but a consequence of it.
Power density of a cell (Lithium, Alkaline or other) is irrelevant for the licking and dying discussion. Batteries catching fire was due mainly to material defects (today we would call them fake batteries - bad copies or rejects that are sold anyway) so it is nothing inherent to the battery chemistry itself. I have been involved in investigation of an EV fire and lo and behold, we found a battery that appeared to have a manufacturing defect that caused the fire.
Back to the licking: your tongue is not a good conductor. Even at 9V it is seldom to see more than a few milliAmps flowing. But your tongue is very sensitive, that is why this harmless current can lead to a very strong reaction by the person that is licking.
If you would cover your tongue in alu foil, then it may be possible to get a large current out of the battery, heat up the foil and burn your tongue. Still not life-threatening.
Lithium batteries have a much higher power density. If a conductive object (or tongue) shorts the terminals it can start a fire. There have been a few inflight incidents on passenger aircraft and one cargo plane accident caused by lithiums. The FAA and TSA have imposed restrictions on Li batteries: http://www.tsa.gov/travelers/airtravel/assistant/batteries.shtm
No - you can't die from licking a 9V battery since even if it would get under your skin (how often do you slice your tongue while licking something???) and the resistance reduces, this will only send a higher current *through your tongue*. Nothing of it will go through your heart, you just get a more painful experience in your tongue.
Change the battery once a year? I have never heard of that and while safety in smoke detectors is a good thing, this makes the waste pile about 3 times larger than it needs to be. Probably the same reasoning as to change engine oil every 3000 miles - it does not hurt the manufacturers pockets and they know that some customers (or sketchy oil change outlets) will skip a change at times and you will still be fine. Why does a USA car need a change every 3k and the same car in Europe has at least 15000 km (about 9k miles) change interval?
Anyway - every smoke detector will start beeping when its battery is getting low. Typically this happens after about 3 years. Keep a spare battery at hand for when this happens at night and you will need way less batteries than when changed every year, or simply change all batteries after 3 years! Note that some detectors include more features than the stand-alone smoke detection, so those may eat batteries faster... YMMV.
I thought I "discovered" this myself, but apparently not. Here's an article called "9 volt battery tongue test." And here's a forum which debates the "can you die from doing this." (Link is here.) I think theoretically you can (if you get beneath the skin, so there's no skin resistance, then current draw will rise). However, in practice this is highly unlikely and I've never heard of it, not even on that cable show "1,000 Ways to Die."
When I was much younger and spent alot of time outdoors we would wrap a 1-1/2 volt "D" cell in aluminum foil and use it as a hand warmer during the cold months. To furn it off you would simply unwrap the foil from the battery, circuit opened!
I used to work in a server validation lab. We would regularly replace the large coin cells on the motherboards and toss them into a large jar. Once, we forgot to empty the jar for a while and got enough "almost dead" batteries to short out and start a small fire. We quickly changed or policy to require wrapping the terminals with tape before we tossed the batteries.
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