Today I needed 4 AA batteries to use together in a critical application where they will be connected in series, and decided to break them out of a never-used, brand-new pack of Made in Japan Panasonic White BK-3MCCA 1900mAh Eneloops I purchased from Amazon in February 2020. They all have an imprinted ‘bas-relief’ code of “19•10MY”, which I think means they were manufactured sometime in October 2019 (so, about 5.5 years ago).
As I always do before using any batteries, I checked their voltage with my Uni-T UT210E multimeter, and all of them were at 1.300/1.301V, except one that measured at only 1.283V; I repeated the measurements and got exactly the same numbers for each one of them.
That’s the first time I see anything like this with supposedly high-quality and genuine NiMH batteries as those Eneloops are supposed to be.
Am I right to presume that something is wrong with that one battery showing only 1.283V, and to avoid using it in series with the other three that are all measuring at 1.300V?
In case anyone is curious, here’s a photo album of me breaking out the pack, separating those 4 batteries, labeling them, and finally measuring them up: https://photos.app.goo.gl/TtiBHpzUnKNmW1Wa6
5 years old, three were THAT close, and only one was a teeny tiny bit discrepant! I’m shocked they were that close, even for Eneloops over that long a time.
It was off 0.017v. That’s trivial.
If it were me, I would check the IR. Charge them up, and check capacity. If all of those measurements are within tolerances/expectations, I would just use them. The resting voltage readings that you got did not show a difference that would be of concern, to me anyway. Especially after them sitting for 5 years.
If you have a charger that can do a full capacity test or even a refresh cycle, I’m inclined to say it wouldn’t hurt to do that after they’ve been sitting for a while, but this doesn’t concern me, especially not with NiMH cells.
I wouldn’t even worry about 0.017V difference on a lithium-ion, although there is a point where enough voltage difference between cells could cause a rush of current trying to equalize immediately upon installation in parallel, or could overdischarge the emptier batteries if used in series.
Consensus seems to be the difference is not significative. I’m still worried because, with same-pack genuine never-used japanese Eneloops, I’m used to seeing differences in the couple-of-mVs (ie, way less than 1%), and so this 17mV / 1.3% difference is an order of magnitude greater; this is corroborated in this particular episode by the fact that I measured all the other batteries in this same pack and they all were at 1.300/1.301V.
Responding to your particular comments below:
Thanks for your opinion, but I do not think so, as they are all came from the same unopened pack, and have all the exact same batch markings (“19•10MY”). Intra-batch differences should be small, in my experience usually in the couple-of-mVs/less-than-1% range as noted above.
Thanks for your opinion, but I’m not worried about “level of charge”; I’m worried about this larger-than-usual difference in out-of-the-same-pack voltage could signal something (internal chemistry, electrode status, soldering quality, etc) is different with that particular battery, and that (when I put it into use in series with the other batteries) could cause unbalancing problems. But I think I get your drift, ie you don’t think this is significant even in these circumstances.
Thank you both for your opinions. It’s just that my experience with these batteries in the same circumstances has consistently showed much smaller differences, as I noted at the start of this message. Perhaps I have been having good luck until now, but I’ve been buying and testing and using these batteries for over 15 years now, and besides I’m not a big believer in good luck.
Thank you @Mandrake50 for your thoughtful and detailed comment, and that’s exactly what I have in mind. Haven’t put them in a charger yet (was waiting to hear from y’all first), but my next steps will be to put all four of them into my Enova S8000 (the best IR-measurer I have here, in my tests it has beaten my MC3000 in spades) and if it shows a reasonably close IR value for that particular battery when compared to the other three, I will then run a couple of Discharge-Charge cycles and compare capacities and final IR values after each cycle. If everything is close enough, I will then write off this difference as some harmless fluke and just go ahead and put them to use.
Thanks for the suggestion! Yes I do, both a SkyRC MC3000 and a Enova S8000, and will do as you say with the S8000, after checking their initial IRs to make sure they’re close enough.
This is exactly what concerns me; as it’s going to be used in series with other 3 batteries which are all in the 1.300-1.301V range, and in a critical application, I was worried it could cause some kind of imbalance between the batteries like you pointed.
Thank you all again for your opinions and suggestions! I will proceed as above and keep this thread posted.
Good thinking. They were all inside the same blister pack – but indeed, the pack could have been impacted sometime during transport and the impact could have been on top of that particular cell. I inspected all cells visually and there’s no physical marks (no marrings, rubbings, ruptured wrapper, dents, etc), so we can’t be sure.
Anyway, my incoming cycle testing should show us that. Will probably start it later today,
As shown in the photo, the battery that was showing lower voltage on the UT210E is also showing lower voltage on the S8000 (my S8000 voltage display is about 0.003V lower than the UT210E with any batteries – haven’t had the time to procure lab-quality equipment and so determine which one needs calibration, so I’m keeping both as they are until I can do that).
More importantly, that same battery is also showing significantly higher IR, about 10% more at 27mΩ vs 24-25mΩ for the others. I don’t think this is a coincidence nor that it should be just ignored, at least not without more tests.
So, what do y’all think? Should I go ahead and cycle-test all four batteries a few times and then compare capacity and ending IR after each cycle among all of them, or do I simply take that lower battery out of the group and replace it with another one from the pack that’s also measuring 1.300/1.301V like the other three?
What is amazing is that they were that close.
What do you do with batteries that you’ve actually used? 10-20 cycles of ANY set of cells, no matter how will matched initially, will likely never be within 5-10% match in capacity or IR again.
I just got done doing capacity and IR testing on about 30 well used AAA. The best of them are lucky to be within 20% of each other. Many are way beyond that.
Cells are consumable. They are dying from the day they are made, use them or not. They simply do not decline at the same rate. Micro variations in construction and macro variations in use create larger differences over time.
Besides, what are you going to do anyway? They are 5 years old out of the package. You have other 5 year old packages to substitute from?
Even if you were to operate on a psychological basis of PURE UNBRIDLED FEAR, ruminating endlessly on the horrible possibilities that might occur? What then? How long would your discussion on the matter persist? How many charge discharge cycles and IR tests would you perform? Do you suppose you could you ever be satisfied with anything less than absolute perfection? And what if the burden of making definitive decisions for yourself is simply too great? Who can you trust? How can you possibly know what’s true? The consequences could be disastrous…
Cycle test them. I don’t think there is any danger. The differences that you are seeing are not alarming. Recheck the IR when they are all fully charged. DC IR varies significantly with state of charge (SOC). So if the cell has a lower voltage (SOC), I am not surprised that the IR would differ a bit for the one slightly undercharged cell. Checking them all when fully charged will give you better (more accurate) idea of what is going on. I vote for cycling them and rechecking.
Maybe I missed it but why is there an assumption that the batteries were all produced at the same time, charged together, etc. It could be that they were produced in different batches, charged on different chargers and so forth.
Again, thanks for your detailed, considered comment. More, below:
When in serial applications, I watch their IR and mAH after every charge, and periodically do a full refresh and watch the MaH there too, and try to keep them paired. It’s actually not hard.
My experience is completely different: with cells grouped from their first use and always used together, and using legitimate made-in-japan Panasonic Eneloops, even after dozens of cycles they are still within 1-2% of each other, both in mAh and IR.
I just got done doing capacity and IR testing on about 30 well used AAA. The best of them are lucky to be within 20% of each other. Many are way beyond that.
Ouch! Unless you are talking about bogus eneloops or the ones made in China, or are talking about really tired cells having gone through hundreds of cycles, that is absolutely not what I’ve seen.
Wait… you are talking about random cells, I mean, cells that were not grouped from their first use and always kept grouped, always going through every charge and discharge together, being stored together, etc, right? Then I can see that happening. But please note I’m talking about grouped cells.
Not sure what you mean, but I do have 16 cells from that same package I just broke out, and almost all of them (with the exception of that single cell) are at 1.300/1.301V as I described. What I will do is simple separate that 1.283V cell to be used separately (ie, in solo applications) and group only 1.300/1.301V cells together – so, no big deal. Sorry if I was not clear before.
I will proceed as above and keep this thread posted.