internal resistace escalation in storage

So, I've a set of 4 Duracell 2650mAh that was previously used. After I brought 'em out, they were reading 1.20v, meaning that they're not completely discharged.

I tried to charge them on a Duracell's own 30 minute charger and two of them are rejected.

Duracell fast chargers run a impedance check and reject cells with high internal resistance, so these two cells escalated in internal resistance enough to be rejected by the charger.

I had the same thing happen to a set of eneloop a few months ago. Anyone experiencing this with previously used cell that were stored for a while?

I haven't seen a refusal to charge, but I do think that 1.20 V indicates the cell is completely empty. When I discharge cells down to 0.9 V on the C9000 and let them rest for a day the voltage on most cells recovers to 1.20 V.

Maybe you could try a short period of charging on a slower charger and then try the fast charger again?

Handlobraesing said:

So, I've a set of 4 Duracell 2650mAh that was previously used. After I brought 'em out, they were reading 1.20v, meaning that they're not completely discharged.

I tried to charge them on a Duracell's own 30 minute charger and two of them are rejected.

Duracell fast chargers run a impedance check and reject cells with high internal resistance, so these two cells escalated in internal resistance enough to be rejected by the charger.

I had the same thing happen to a set of eneloop a few months ago. Anyone experiencing this with previously used cell that were stored for a while?

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Some chargers will reject a cell if the voltage is too low like 0.2 volts or reversed voltage. My LaCrosse and my Maha 808 will reject cells with low voltage as bad cells.

Many times a cell in a series of 3 or 4 will become disproportionally discharged, and sometimes reversed, but they can be saved.

I have a charger that doesn't reject them and so I will put the cell for just a minute or two on a Tenergy T6278 which will rapidly bring the cell up to 1.0 volt, then it gets accepted on the others.

Mr Happy said:

I haven't seen a refusal to charge, but I do think that 1.20 V indicates the cell is completely empty. When I discharge cells down to 0.9 V on the C9000 and let them rest for a day the voltage on most cells recovers to 1.20 V.

Maybe you could try a short period of charging on a slower charger and then try the fast charger again?

Click to expand...

You're right they're probably discharged enough to be unusable without charging. What I meant is that there is no fault causing to drain to the ground, meaning, measuring 0v, which happens sometimes.

I had a set of eneloop go bad like this not long ago too and now a set of Duracell 2650mAh AAs that was only used a few times. This set was stored together, not installed in anything.

Handlobraesing said:

I had a set of eneloop go bad like this not long ago too and now a set of Duracell 2650mAh AAs that was only used a few times. This set was stored together, not installed in anything.

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I'm not following you around, picking on you or anything (well, OK, maybe a little bit ) Handlobraesing, but I mentioned in the eneloop thread that possibly, if you have ever drained your NiMH's down to zero Volts, or even near to that, the resulting damage to the cells may be the problem. Especially, if it happened on multiple occasions. NiCd's can handle that reasonably well, but not NiMH's. Were these ever drained flat?

Just trying to help figure this out.

Dave

45/70 said:

I'm not following you around, picking on you or anything (well, OK, maybe a little bit ) Handlobraesing, but I mentioned in the eneloop thread that possibly, if you have ever drained your NiMH's down to zero Volts, or even near to that, the resulting damage to the cells may be the problem. Especially, if it happened on multiple occasions. NiCd's can handle that reasonably well, but not NiMH's. Were these ever drained flat?

Just trying to help figure this out.

Dave

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Not beyond ordinary expected use, such as using it until "low batt" shows up on my camera.

TorchBoy said:

I'm with Mr Happy - if they read 1.20V they're fully discharged. Did you abuse that Eneloop much? (I mean treatment, not verbally after you found it didn't work.)

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Over discharging we're talking about is letting it drain to 0v or going into reverse polarity. Healthy end of discharge voltage is 1.0 or 0.9v on NiMH.

These cells were not drained to the ground externally. These had partial charge and left sitting around for a few months, something they should be able to tolerate. I have actually had this happen to NiMH as well. Maybe there's something about NiMH/NiCd not being able to tolerate extended storage once they've been used?

The NiCd I had the same problem with is a NiCd pack for a Makita drill. The pack was used a few times, but one pack was adequate for what I did, so the other pack was stored away for a year or two then when I tried to use it, it was no longer accepting fast charge.

I'm with Mr Happy - if they read 1.20V they're fully discharged. Did you abuse that Eneloop much? (I mean treatment, not verbally after you found it didn't work.)

Handlobraesing said:

Not beyond ordinary expected use, such as using it until "low batt" shows up on my camera.

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OK, well that should be perfectly normal. Humm. I'm starting to wonder about any of the high cap NiMH's. First it was the Energizer 2500's performing badly. Now I hear about some Sanyo 2700's having similar problems and I think somewhere saw where Powerex 2700's were in question.

I too go along with Mr Happy and TorchBoy on the discharged voltage. 1.20 rested, open circuit pretty much parallels 0.9-1.0 Volts under load, in my experience.

Carry on Gentlemen,

Dave

45/70 said:

OK, well that should be perfectly normal. Humm. I'm starting to wonder about any of the high cap NiMH's. First it was the Energizer 2500's performing badly. Now I hear about some Sanyo 2700's having similar problems and I think somewhere saw where Powerex 2700's were in question.

I too go along with Mr Happy and TorchBoy on the discharged voltage. 1.20 rested, open circuit pretty much parallels 0.9-1.0 Volts under load, in my experience.

Carry on Gentlemen,

Dave

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I think damaging discharge would be discharging to the point of polarity reversal of at least one or more cells in use, or storing it connected to something with the power on or something with a parasitic draw and draining them down to 0v.

NiMHs are not Pb acid, therefore there is no requirement to be kept fully charged and I'd rather not deal with 2650mAh cells if they're going to be high maintenance.

I have read that if NiMH cells are stored in discharged state then one of the electrodes can suffer some kind of irreversible chemical degradation. NiMH are different from NiCd (which can be stored empty) in this regard. [Edit: Following SilverFox's comments below I re-checked the technical literature from several manufacturers. All of them say that storing NiMH cells in a discharged state causes no harm. There is no irreversible chemical degradation.]

What I read is that NiMH should be stored with a medium charge and should be checked and topped up every few months to keep them in good condition. [Edit: Again I didn't get this quite right. What the manufacturers say is NiMH cells can be stored in a charged or discharged state, it should make no difference to storage life. However, after a period of time there will be a temporary loss of capacity; so every six months to a year the stored cells should be put through one or more charge/discharge cycles to get them back to 100%.]

Of course LSD cells should manage much better than this in storage, since they should not self-discharge down to zero in just a few months. In fact, I have an unopened pack of Eneloops with a date code of May 2006 which I hope to test in May of this year to see what charge they hold. I'm predicting it will be about 1300 mAh.

[Edit: Of the different sources I looked at, this one seems to be a particularly thorough and informative overview of the handling, charging, storage and maintenance of NiMH cells: http://www.hardingenergy.com/pdfs/NiMH.pdf]

Hello Mr Happy,

To keep cells in storage vibrant, store them discharged, and do a charge/discharge cycle every 30 days.

This goes for most NiMh cells, but some of the high capacity cells have higher than normal self discharge rates. These cells need to be stored fully charged and recharged every 30 days. Even then, they may drop below 1.0 volts open circuit due to the self discharge rate. They work great hot off the charger, but the high self discharge rate is an issue.

NiMh battery packs used in high performance lights and power tools require a little different care. If they are in constant use, there is usually few problems other than keeping the cells within the pack balanced. However, there are major issues with stored packs. Most people want to store a pack fully charged. This leads to poor performance when you finally get around to using the pack. On the other hand, a completely discharge pack won't help much for those spontaneous projects that crop up from time to time.

I have been working with three separate contractors over the last two years. Their battery pack inventory includes around 30 battery packs each. These guys typically have 10 - 15 battery packs for their power tools die on them each year. The first year, after re-training, we saw those numbers cut in half. Last year they had no battery pack failures.

I expected an improvement, but I was very impressed with our results.

If our good results continue this year, I will have established a pretty good track record for battery pack storage and maintenance.

The old procedure was to charge them up and store them fully charged. The revised procedure involves, among other things, storing them in a discharged state and to recognize when they needed to put the pack on the charger to be ready to go when they needed it. With some of the crews, we ended up putting a little charge back in, and that is what I do with my power tool battery packs. This allows me spontaneous use of my tools, but I have to remember to charge my pack before extensive use. I have not found this to be an "issue."

There were a few hiccups during the implementation, but the results seem to indicate that we are on the right track.

Tom

SilverFox said:

Hello Mr Happy,

To keep cells in storage vibrant, store them discharged, and do a charge/discharge cycle every 30 days.

This goes for most NiMh cells, but some of the high capacity cells have higher than normal self discharge rates. These cells need to be stored fully charged and recharged every 30 days. Even then, they may drop below 1.0 volts open circuit due to the self discharge rate. They work great hot off the charger, but the high self discharge rate is an issue.

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Why is it I don't seem to have an issue with Duracell 2650mAhs that were never used and stored for months?

I'm cycling the previously used(a few times) and stored cells on MH-C9000 repeatedly but they're still not looking too happy

I wonder if this same phenomenon is what happened with my 2100 mAh ROV cells.

I did the break in on the C9000 and the results were pretty bad. I put them on a conditioning cycle on my C800S last night and then did a discharge cycle on the C9000 this morning.

The capacities of the cells tested so far (the other 4 are being discharged on the C9000 right now) dropped about 100 mAh from what the break in cycle reported.

Hello Black Rose,

I believe you should get the highest capacities from the break in run.

Tom

Thanks Tom.

I took the numbers I got from the C9000 and sent a message off to Rayovac telling them I used their charger on their cells and that they lost 32% to 40% of their capacity in the 6 months I've been using them.

Those were the newest and best treated non-LSD ROV cells I have and they lost the most capacity :thumbsdow

Technically any warranty I had on the cells is void because I put them on the C9000, but it will be interesting to see what they say about it.

SilverFox said:

Hello Black Rose,

I believe you should get the highest capacities from the break in run.

Tom

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Have you done any testing on failing 2650/2700 mAh cells?

Handlobraesing said:

I had a set of eneloop go bad like this not long ago too and now a set of Duracell 2650mAh AAs that was only used a few times. This set was stored together, not installed in anything.

Click to expand...

It's sounding more and more like you have an acute case of resistentialism Handlobraesing.

Even worse, it's appears to be a strain that is especially resistent to all but the most extreme anti-resistentialism protocols.

In your case, I would recommend at least three weeks on a tropical island sans all electrical devices, especially those that are battery operated...

Hello Handlobreaesing,

I have some Sanyo 2700 cells that Aircraft sent me. They are actually very good cells as long as you use them right away. They are suffering from high self discharge, so they can't be stored for use tomorrow.

They still are accepted by the 15 minute chargers, so I don't think their internal resistance is a problem.

Tom

Bones said:

an acute case of resistentialism

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When cells deliberately go high resistance. :laughing: