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Weak AA lithium cell in group of 3?


RPSharman
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Hello,

 

I'm hoping someone can give me an answer without shuffling me off to read books and articles on batteries and circuits.  You know who you are!!

 

I like to deplete my AA lithium batteries before disposing of them.  My method has been to use them in my 3AA-battery-operated LED light I use on the follow cart when AC is not available.  But I am now beginning to collect quite a few used lithium batteries, even though I mostly use rechargeable batteries.  It got me thinking... If I am using multiple lithium AA batteries, which have been previously used for different periods of time, in the same piece of electronic gear (remote control, LED lights, etc.), what effect does the weakest cell have on the others?  Does it matter if the batteries are in serial or parallel?

 

I'd like to know that if the light dies, it means all three batteries are dead, and it isn't because the weakest cell is dead and the other two still have some power.  And I don't want to meter batteries all the time.

 

Thanks,

 

Robert

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We just put them in a "used Lithium AA" box, and I stick them into remote controls and other household items. If I get a couple days use out of them, great. 

 

I have a little "Battery Charge Center" cubbyhole of my house where I keep all the chargers and battery-checkers handy, and I'll go through the batteries every so often. As we all know, the Lithiums go right off the cliff very fast without much warning, so I'm reluctant to employ a used Lithium on any significant shoot. I just had two events in a row -- three daily live shows and then a 2-hour live audience lecture at the ASC -- where we had zero tolerance for failures. Total cost to me: $10 in AA's. In any kind of scripted situation where I could get in and swap out rechargeables, I'd definitely use those. But I'm still running into 50% runtime differences with the Powerex's, a problem I have yet to solve.

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http://www.ztsinc.com/military.html

 

I have this $145 mil-spec battery tester for accurate testing of lithium batteries. Its microprocessor controlled, and takes about 5 seconds to evaluate a lithium battery.  It's the only model that will test 9V lithiums, but if you don't use 9V lithiums, there's a $70 version available everywhere. 

 

Except- get this-  I've learned to truly evaluate each AA, I run the test 4 times (manual recommends at least 2) If the AA shows anything less than 100% after 4 tests, I don't use it in anything demanding. 

Also any Lithium AA- even a fresh one-  will show less that 100% if tested immediately after being removed from any device.  

 

This is definitely a weekend-type process.

 

My 13 year-old does the testing. My IFB's haven't seen a new battery in four years.

 

With the mountains of AA lithiums that many shows discard, or the routine replacement of AA's on a daily basis, hundreds of good lithiums get tossed, except when I'm around...

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" You know who you are!! "

yes, I do...

but this is really basic electronics

in series: " the weakest cell will die first and leave the others with charge capacity remaining, "

in parallel, not so much.

I have several single AA cell miniMag lites for using up AA's...

Multi-meters measuring volts are , er, OK, maybe, but a tester that measures under a load is better.

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" You know who you are!! "

yes, I do...

but this is really basic electronics

in series: " the weakest cell will die first and leave the others with charge capacity remaining, "

in parallel, not so much.

I have several single AA cell miniMag lites for using up AA's...

Multi-meters measuring volts are , er, OK, maybe, but a tester that measures under a load is better.

 

Of course, under load will tell you more.  Testing the battery with a full-on, high-end battery tester will tell even more, and plotting the battery's discharge curve as you completely deplete it will tell you the most (rendering the battery useless, of course) -- but Robert wanted the quickest, most efficient method of using up remaining battery life and the quick voltage test and sorting method I mentioned is how I do it.

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I have this $145 mil-spec battery tester for accurate testing of lithium batteries. Its microprocessor controlled, and takes about 5 seconds to evaluate a lithium battery.  It's the only model that will test 9V lithiums, but if you don't use 9V lithiums, there's a $70 version available everywhere. 

 

Wow, that is impressive! I honestly didn't know there was something that could actually get meaningful information out of a Lithium beyond "it's good" or "it's almost dead." 

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  • 2 weeks later...

Kirchoff's Law doesn't apply to lithium batteries?

It does apply in this and any other case I can imagine. Friendly question- What was posted that made you think someone was saying it didn't?

The comment about fully depleting the batteries was that, in series, you couldn't deplete them all without one or more cells being reversed in voltage leading to possibly dangerous conditions. A reversed alkaline at high current builds up pressure and spews electrolyte. A reversed lithium might be worse. In most cases, the device it is in draws low current and the reversed battery just generates a little heat.

Best Regards,

Larry Fisher

Lectrosonics

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