Alkaline batteries

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sTeamTraen
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Alkaline batteries

Post by sTeamTraen » Sun Aug 08, 2021 2:50 pm

I have a small movement-activated light that I use as a night light in the bathroom. The other day I noticed that it was very weak, so I went to change the batteries (3 x AAA alkaline). But I thought I'd test them with a voltmeter first to see if any were salvageable.

The voltages were 1.38, 1.39, and minus 0.34. I changed just the negative one and now I've getting near-new performance.

I've had this happen more than once over the years (being a cheapskate, I always test batteries before throwing them out). Why would an alkaline cell "go negative" like this?

Supplementary: Is there anything about alkaline batteries that can sensibly be recycled, and/or a reason why they should not go into a municipal incinerator or landfill? I remember many years ago when I lived in the Netherlands the recycling info sheet said "Just put them in the bin with the other non-recyclable stuff", but maybe techniques have moved on since them. I notice that the boxes for batteries to be recycled in the supermarket are mostly alkaline these days, whereas it seems that the main environmental aim is to recycle (or keep out of the groundwater), nickel, cadmium, and lithium. The little button batteries all seem to be alkaline instead of mercury now too.
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Martin Y
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Re: Alkaline batteries

Post by Martin Y » Sun Aug 08, 2021 3:00 pm

I don't know the chemistry but when one of the batteries fails and can't produce the current required of all 3, its voltage collapses and the current that's still flowing from the good batteries keeps passing through it and (presumably very inefficiently) begins to charge it up in reverse.

IDK if there's significant commercial or environmental benefits to recycling alkaline AAs or AAAs but I still take them to Tesco and let them decide what to do with them.

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Martin Y
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Re: Alkaline batteries

Post by Martin Y » Sun Aug 08, 2021 3:10 pm

Button cells are almost all alkaline nowadays. You can still get the silver based equivalents but they cost several times as much and usually only go in things like watches where changing them is a pain so the longer life is worth it. Mercury types are a tiny niche product that might still be available for old models of hearing aids but I haven't seen any for years.

WFJ
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Re: Alkaline batteries

Post by WFJ » Sun Aug 08, 2021 3:29 pm

sTeamTraen wrote:
Sun Aug 08, 2021 2:50 pm
The voltages were 1.38, 1.39, and minus 0.34. I changed just the negative one and now I've getting near-new performance.

I've had this happen more than once over the years (being a cheapskate, I always test batteries before throwing them out). Why would an alkaline cell "go negative" like this?
If you normally change the batteries one at a time, rather than as a whole set, this is probably why one of the batteries reversed.

Edit: I should read the thread before replying.
Martin Y wrote:
Sun Aug 08, 2021 3:00 pm
I don't know the chemistry but when one of the batteries fails and can't produce the current required of all 3, its voltage collapses and the current that's still flowing from the good batteries keeps passing through it and (presumably very inefficiently) begins to charge it up in reverse.
This.

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Boustrophedon
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Re: Alkaline batteries

Post by Boustrophedon » Sun Aug 08, 2021 3:32 pm

Martin Y wrote:
Sun Aug 08, 2021 3:10 pm
Button cells are almost all alkaline nowadays. You can still get the silver based equivalents but they cost several times as much and usually only go in things like watches where changing them is a pain so the longer life is worth it. Mercury types are a tiny niche product that might still be available for old models of hearing aids but I haven't seen any for years.
You can't get mercury cells at all except if you are lucky and find old stock. Owners of original Bulova Accutrons have to get their circuitry adapted to work on modern silver cells, because the voltage is not the same.
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WFJ
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Re: Alkaline batteries

Post by WFJ » Sun Aug 08, 2021 3:44 pm

Boustrophedon wrote:
Sun Aug 08, 2021 3:32 pm
Martin Y wrote:
Sun Aug 08, 2021 3:10 pm
Button cells are almost all alkaline nowadays. You can still get the silver based equivalents but they cost several times as much and usually only go in things like watches where changing them is a pain so the longer life is worth it. Mercury types are a tiny niche product that might still be available for old models of hearing aids but I haven't seen any for years.
You can't get mercury cells at all except if you are lucky and find old stock. Owners of original Bulova Accutrons have to get their circuitry adapted to work on modern silver cells, because the voltage is not the same.
Zinc-air batteries are often used as replacements in old cameras/light meters as they provide a similar voltage to mercury. They're probably not great for watches though as they only last about six months once opened to air, regardless of use or load.

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