"Touching (one or both terminals of) button batteries causes them to discharge" - any truth?

[NY]

My wife has always believed that if you touch both (and maybe just one) terminal of a flat disc "button" battery (eg CR2032, CR1620 as used in a watch, key fob, PC BIOS), you will cause the battery to discharge, so you must take care when fitting a new battery not to "short the terminals with your fingers".

I can imagine that sweat on the metal terminals *may* cause a bit of oxidation over a long period of time, but I can't see how a body resistance of many kilohms will cause the battery to go flat.

Is there any truth in what she's always believed and what she advises me to do?

[The Natural Philosopher]

'Short' is a binary term for something that in this case is far from binary.

typical resistance between fingers will be in he several hundred kilohm range. Not enough to upset a low voltage battery.

Two wet fingers across my multimeter got me about 180k Note that 30mA is RCD trip current for safety, so that implies a human body might be somewhere on the 50mA at 240v = 4.8K region worst case with two hands wrapped around conductors...

I managed to pickup a live lamp-holder I was working on the other month and got a nice 'trembler' Didn't trip the RCD...

[Martin Brown]

Bridging the insulation between the positive and negative terminals with a sweaty fingerprint will shorten the battery life somewhat. But it would have to be a very low capacity battery for holding onto the terminals for a few seconds. Very few people are lower than 50k skin resistance and some are as high as 10M.

Biggest danger from them is children swallowing them which can cause very serous internal electrolytic burns.

There is truth in the don't put a fingerprint across the insulation that separates the two terminals. Much like don't put fingerprints onto quartz halogen bulbs - the sodium chloride and skin oils cause trouble.

[JohnP]

"NY" [e-mail] wrote in news:rl9lcl$vcp$ [e-mail]:

I have always follwed that advice.

[Jim GM4DHJ ...]

bollox...but you need to keep them clean ....

[Brian Gaff]

No not really. Some small button cells have a tiny hole with a sticker over it which activates it and then its age is limited. I think the ingress of air is needed, but I'm no chemist. The main problem with those batteries is contamination from your fingers. You should but I seldom do, handle them using cotton gloves to stop the grease getting on them. Because the current drain from them is small, any kind of build up of resistance can make them crackle as the terminals oxidise or the muck gets in. Brian

[John Rumm]

I think this is one of those old wives tales that started with a grain of truth, but then the actual detail got lost along the way, and now the "fact" recalled is nothing to do with the actual issue[1]

Indeed. Things like button cells can be used in applications where they will last years, so making sure there is no contamination of the surfaces makes sense. However you will not drain any noticeable energy though your fingers while poking it into its socket.

[1] Bit like when people try to tell you that turning on a fluorescent light will use 15 mins worth of electricity. The real deal is that starting a lamp will use up some of the life on the heater coils, and eventually could cause a lamp to fail to start - thus raising the overall costs per hour..- but drawing 15 mins of energy in the couple of seconds required to start it, is something the circuit breaker might have a thing or two to say about!

[tabbypurr]

I once did a calcualtion on that & concluded that the total costs of leaving a linear fluorescent light on were only beneficial for a matter of seconds, beyond that it was cheaper to switch off. A molehill had been made into a mountain somewhere.

NT

[Harry Bloomfield, Esq.]

NY formulated on Saturday :

It's the sweaty/oily deposits from your skin which is a problem, it can short across the insulator and cause the low power cells to discharge and reduce their working life. You should only touch them with insulated tweezers, to avoid this.

[The Natural Philosopher]

Utter bollocks

[Harry Bloomfield, Esq.]

The Natural Philosopher has brought this to us :

Your skin deposits are conductive. Were that no so, you would be unable to receive a shock when touching mains voltages, nor would you leave fingerprints behind, on everything you touch.

[tabbypurr]

Semi-true. As an argument for not touching batteries it's a nonstarter.

[The Natural Philosopher]

but they are only conductive when wet, and fingerprints are oils, not water based solids

And the water based parts dry out.

[Paul]

The cell consists of two corrosion-resistant surfaces, and an air gap. Below the air gap is some dielectric material which does not conduct.

To discharge the battery requires shoving a significant amount of material into the insulating gap.

The only reason for keeping finger oils off battery contacts, is in the belief it will lead to unreliable contact with the terminals. The socket materials are not as good/expensive as the cell materials.

While you might drop the cell several times while handling it, it's not likely to have a "deep discharge" event.

Some cells are knackered in the package. I was sold a CR2032 at the mall, which was dead about a day after I got it, which meant the product had been sitting in that store for 10+ years. Or, it was a counterfeit of a very inferior nature. No amount of fingerprints would be responsible for that. Another cell purchased elsewhere, behaved properly. It's not like I had premature failures one after another, just the one cell that was knackered, out of the package.

Paul

[Chris Green]

All the button cells I have bought in the last few years have 'use before' dates on them (or something like that).

[Tim Lamb]

In message <rlahvv$1mtk$ [e-mail]>, Paul [e-mail] writes Snip

Some battery powered devices have a constant battery drain despite being

*switched off*.

My two are a pistol grip laser thermometer and a digital vernier gauge. Left connected, 4 weeks battery life:-(

[PeterC]

Verniers are bad for that. I have an Aldidl one that takes a an LR4 and would last a few months at most. Although I didn't 'need' it I got another one from Aldidl that takes a CR2032, thinking that the bigger cell should last a lot longer; it doesn't!

BTW, I've a vernier caliper that doesn't take a cell but I can no longer read it very well. If someone wants it, drop me an e-mail - free to a good home where it'll be used.

[Brian Gaff (Sofa]

Of course there is always waste, both in the form of heat and sound from those lights, depending on the way they are started and if it has a gynormous choke or not. Many of the so called low energy fittings and lamps tend to spew out RF which is basically wasted. Hum from the choke, and heat in the starter bulbs loses energy.

I guess you could design some very kind starters for them, indeed the old battery ones suggest to not even use the heaters, at least not on the one I had it just developed a very height voltage till it started, then lowered it to the most efficient running voltage when conduction was in progress. They still got tired though and would enter that flash on and off behaviour, first noticeable in the cold. I'd imagine the particles inside did something to the electrodes and or the phosphor on the inside of the tube after some time. Brian

[Brian Gaff (Sofa]

Yes, I've had the old black pea in a pack. I did send it back and got a free new pack. No mention of fake. This was the old Energiser brand, used to be Ever Ready I'd imagine, which when you think of it was a lie in the name, as in the old days, even when they rebranded to Berec was not true. Most Japanese batteries of the same era outperformed them. Duracell outperform Energisers as well, indeed Sainsbury's own brand out perform energisers! Brian

[Andrew]

Renata (switzerland) used to be the battery of choice for cameras back in the days of film when silver oxide batteries were needed.

Andrew