Reviving New Old Stock (NOS) NiMH AA cells

Batteries and Chargers Rechargeable Batteries
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Over the last week or so I spent some time experimenting with some new old stock nickel metal hydride AA cells that I had come across.
About 10 years ago or so, before there was a BLF, before I even knew there were others just like me, I was just a lone wolf in the wilderness enjoying my passion for flashlights and rechargable cells. Back then, to me, Nickel Metal Hydride cells were the upgrade to the old NiCd cells that I was using up until then. Of course they were expensive and I was always looking for a cheaper way out, always looking for a bargain. As it was, I came upon a local retail store, “Ocean State Job Lot” that specializes on distressed and “odd lot” type of merchandise. What I came across was some NOS cordless phone batteries. Now this was 10 years ago, and these batteries were NOS then. That would make them ancient today. The other day, while organizing the basement, I came across an old package of one of those cordless phone batteries. 10 years ago I paid 50 cents for this package.

Most cordless phone batteries look something like this.

In this case it is a pack of 3 - AAA cells welded in series for 3.6V pack. Back then I would break apart the cells and get 3 separate AAA cells for cheap. In this case 3 - 750mAh cells for 50 cents.
But the cells that I will be testing are from the first pack above. In that case, they are just 2 separate AA cells, just as you would buy for a flashlight. Back then, getting 2 cells for 50 cents was a very good deal. That is why I bought 12 packs of 2.

Each of those 2 cells is only rated at 1300mAh, not much by today’s standards, but hey, the price was right.
That’s the back story, now on to my little experiment.
Remember now, those cells were NOS when I bought them 10 years ago so I am guessing they are 10 - 15 years old now. When I first found them cleaning the basement, I was going to just throw them out, but instead I decided to test them out.
I opened that pack and measured each cell. They both read 0.80V. I was very surprised that they weren’t at 0. So I put them in my OPUS BT-3100 and charged them up. Just a couple of minutes later, they were finished! All charged up.
Of course right then I knew that they would have a VERY low mAh capacity. In fact they rated as such when I discharged them thru the OPUS. For those that don’t know, the OPUS is capable of discharging and measuring the total mAh draw of a cell. Some, if not most of you know that NiMH cells can sometimes recover “lost” mAh’s thru “exercise” That is thru several charge and discharge cycles. In fact the OPUS is capable of doing just that, performing several cycles of charging and discharging in an attempt at recovering lost mAh’s. “Just set it and forget it” :slight_smile: The only downside of this automatic routine is that you don’t get to see the progression of the improvement. BTW, this only works for NiMH cells. Not Li-ion
So with it being around the holidays, I decided to use the OPUS to manually charge and discharge these 2 cells and chart the progress. If there was improvement, I would repeat the cycle. Each time recording the results. All charging was at 500mA and all discharging was at 700mA
Initial resting voltage of each cell after having been in the package for 10+ years was 0.80V


At this point I noticed a dip in cell B, so I went for broke. What would happen if I drew 7A off these fully charged cells? Would that damage them or make them perform even better. So I did a discharge at about 7A for about 30 seconds. Then I recharged them and continued with the tests.

At this point I let them “rest” in a discharged state for a couple of days. (Actually, I had better things to do :slight_smile: )Then I charged them up again and continued the test.

1300 957

This test was notable in that cell A actually performed at it’s rated capacity when brand new!

Clearly cell B is not up to snuff, but can I revive it further? There is still progression and I will try later. Also to do is test the self discharge rate of these cells. I am expecting that it will be rather high, a usual problem with older NiMH cells and probably worse for these as they are quite old.
Also another test I am in the process of doing is seeing how far I can revive some of these same exact cells that have seen service in the past. They are the same age as these, they are just not NOS.

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Interesting and thorough test. :slight_smile: The same batteries are still for sale on Amazon Canada! There is a UK listing by the same seller that was created in 2006. It looks like these would have been sold at a premium over ‘normal’ nimh AA rechargeables. I do find it quite surprising though that they still work at the as new ratings after the recovery process.

Anyway, looks like I don’t have to worry about the unused eneloops I have though . :slight_smile:

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I fixed the formatting the best I could. Boy I wish I could learn how to use the advanced editor!

My BIG take away on this is that it is a better strategy to have few cells and work them hard, recharging them every day as they are drained. Better than having lots and lots of cells that see infrequent use!

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I happen across a fair amount of dirt-cheap dusty NOS cells like these but was always too wary of them to try this. Perhaps you’re onto a super-cheap source of cells for those who can use the old technology and have a charger which can “wake them up” from their ancient slumber. When it’s useful, cheap always makes it better!

Phil

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This interests me as I'm currently trying to revive some new Tenergy platinum sub c cells I got from Battery Junction this past April. I never checked the voltage on receipt but tried to put them in a light yesterday and found three of the four at 0 volts and the fourth at 1.06. Not sure how that happened but nothing I do to them now can hurt them more.

Some progress has already been made on the Opus refresh cycle and once through the cycle and "fully" charged I sort of blindly discharged the three that got to zero in a triple nichia 219c maglight. The cells put out over 9 amps without a problem and I put them back on the refresh cycle. Guess I'll just keep working them out and see what happens.

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Interesting. How do you discharge them at 7 amps?

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Haha, you would wonder that.

I used a cheap meter with 14 gauge leads to measure the current drawn across the cell shorted with a suitably long piece of 18 gauge wire. :slight_smile:

EDIT:

Your question just got me wondering. Because the 7A draw improved improved the performance even further, I measured the current flow again thru that same piece of 18 gauge wire. Now each cell will push 11A!
I only allowed that 11A current flow for a second though, at this point I do not want to ruin these precious cells. They are an important part of my ongoing experiment. :wink:

8

Interesting read up.

Looking forward to more testing!

We just put some eneloops in a 25 year old remote controlled car, and it was riding as never before. In all those 25 years it had never been so fast probably ;)

Anyhow very interesting to read about the cells, keep us updated.

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These 4 cells are identical to the first 2. The difference being that instead of spending the last 10 years unopened and still in their packaging they have been lightly used. That is they have spent most of the time in the drawer, but they were occasionally used in lights and cameras.

When I first put them in the charger the one to the rightmost, Cell “D” was at 0 volts and was not recognized by the OPUS. What I did was use an old “trick” that most would know about. I “zapped” it. That is I hit it with a short burst of high current. In this case I used a charged IMR 18650 cell and hooked it positive to positive and negative to negative to the dead AA cell. I did this a couple of times, but only for an instant each time. That did the trick and “woke” up the cell.
During the testing, I performed this zapping to each of the other cells. Each cell at a different cycle of the tests, just to see the effect. In the chart below there is the letter “Z” next to the trial when the cell was zapped. The result is the result AFTER having zapped that cell. In other words, the cell was zapped while totally discharged from from the trial above, then charged and discharged. The result to the left of each “Z” is that result.

At this point there doesn’t seem to be much more progression in these used cells. Later I will try shorting them out across that length of 18 gaugle wire and see if I can coax any more performance out of them.

Also coming up will be some more tests on the first 2 NOS cells. Cell “A” seems to be fully recovered, what I want to do is see if I can revive Cell “B” even further.

So what am I doing here? What is this all about?
This clip from “Princess Bride” pretty much sums it up. :bigsmile:

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Thanks for sharing your experiences, I’ve done some testing with old NiMH batteries in the past, and reading other results is interesting.

From what I read, the “zapping” of old batteries is supposed to break down crystals in the batteries, which cause high internal resistance. The high internal resistance means the cells can’t deliver high currents. From my experience, it also means that charging is less efficient. It also means that the voltage that the charger measures rises faster, and could mean that the charger just stops charging sooner, leading to less capacity. If you have an old dumb NiMH charger, you could try charging with that for some amount of time and then measuring the discharge capacity with the Opus.

Have you tried the internal resistance measuring function of the Opus? From what I read it’s not that accurate, but it could be interesting to see whether the internal resistance improves after “zapping” the cell with a high current for a short time. It could be that discharging with a high current has the same effect as charging with a high current. But when the internal resistance is high, the cell can’t supply a high current, and a high charge current is still possible to achieve.

It’s nice to see that you managed to restore such old cells. I’ve had less luck with more recent NiMH cells that were new in pack but completely dead (0 Volt), even zapping didn’t improve things. Maybe the newer (non-LSD) high capacity cells are more fragile. Or maybe the cells were just lower quality.

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Sometimes NiMH batteries are surprisingly resilient. A while back I picked up a handful of AAA Eneloops in a little old Radio Shack (aka ‘The Source’ here in Canada) that was closing out. They’d hung in full sunlight in the shop window so long that the blister packs were faded almost beyond readability. Who knows what temperatures they’d endured for the previous 6 years or so.
Since I got them so cheap (8 for $1, or some ridiculous thing!), I took them all. Every one still tested as still having full initial ‘shipping’ charge, and all broke in at above their stated rating. Needless to say, I was very impressed.
While I keep my batteries in numbered batches and use & charge them in discrete groups as to which device they’re used in, I no longer give any thought to the numbers of cycles they’ve been used. They just seem to keep on going.

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If I recall the “best” way to revive nickel based cells is a slow discharge to around .4 volts then a charge and repeat until needed. More details outlined at Battery University here. I’ve done it on a number of nicads, some come back pretty good, some not so much. I want to try that high discharge trick, it seems if the purpose of refreshing is breaking up the large crystals that might help. Zapping is the process of burning off whisker shorts that pierce the separator. While it works on batteries that have a high self discharge those whiskers often reform in the same holes so the effect doesn’t last super well, I wouldn’t do it unless the self discharge is high it could do more damage than good on cells that have low capacity (large crystals) but no shorts (whiskers). Also every cell I’ve zapped (with a welder) didn’t show any improvement.

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Nice review, pretty solid batteries concerning the age 8)