Degrading eneloop/duraloops

[jhellwig]

I have 4 eneloop AA and about 10 duraloop AA. They have not seen much use and have sat fully charged for quite a while on and off. Maybe a month or two at a time and then get cycled thought the c9000. I have noticed that some of them are dropping below 1900mAh. Cycling isn't improving them either that much. When they were new they were all close to 2000mAh. Most of the cycles that they have gone through is through the c9000. Most have probably been run clear dead maybe once.

Is this a downfall of the lsd sitting full and unused for intermittent periods that is causing the cell to lose capacity? I know that these cells are 07 vintage but is there something to being chuck full that is hurting them.

 

[45/70]

...... Most have probably been run clear dead maybe once.

This is likely the problem. SilverFox has a thread around here somewhere pertaining to running LSD cells, eneloops specifically, to a lower voltage than recommended. As I remember, the jury is still out on whether or not this is more, or less damaging to LSD cells, than standard NiMH cells.

With standard NiMH cells, running them to near zero Volts, can have a permanent, adverse effect on their performance. If the discharge includes reverse charging of one or more cells during the discharge in a series application, this will pretty much kill a standard NiMH cell. LSD cells, maybe not so much, but it is still damaging to the cell. In either case, the effect is cumulative, and cannot be reversed.

All in all, considering the circumstances, your cells are still in pretty good shape. Have you tried a "break-in" cycle on them. This can restore cell capacity better than basic cycling.

Dave

 

[flatline]

What's the threshold? My Quark AA shuts off when the cell voltage is 0.8v (I think...maybe it's 0.9v). Is that too low?

--flatline

 

[Battery Guy]

I have 4 eneloop AA and about 10 duraloop AA. They have not seen much use and have sat fully charged for quite a while on and off. Maybe a month or two at a time and then get cycled thought the c9000. I have noticed that some of them are dropping below 1900mAh. Cycling isn't improving them either that much. When they were new they were all close to 2000mAh. Most of the cycles that they have gone through is through the c9000. Most have probably been run clear dead maybe once.

Keep in mind that 1900 mAh is 95% of the rated capacity. I don't know how much below 1900 mAh your cells are, but let's assume worst case that they are at 1800 mAh (if they were below that, I would guess that you would have said so...correct me if I am wrong). At 1800 mAh you are still 90% of original capacity...after 3 years. Quite frankly, it sounds like your eneloops are performing admirably.

Is this a downfall of the lsd sitting full and unused for intermittent periods that is causing the cell to lose capacity? I know that these cells are 07 vintage but is there something to being chuck full that is hurting them.

As a general rule, the higher the state of charge, the faster irreversible capacity fade will occur. However, you need to keep in mind that all cells degrade with time, irrespective of brand or chemistry, even eneloops. In my opinion, if you are expecting less than 10% irreversible capacity loss every 3 years, you are expecting too much. I would not expect any NiMH, LSD or not, to perform much better. Nor do I think that you are accelerating the demise of your eneloops significantly by storing them at top of charge. After all, isn't that one of the advantages of eneloops, that you can charge them, store them, and know that they will have significant capacity when you need them?

One thing that you should understand is that cycle life testing is performed under non-realistic conditions. For example, when Sanyo claims that their eneloops can be cycled 1000 or 1500 times, they are basing this on continuous charge/discharge cycles testing that occur with little or no time between cycles. If you are only cycling your cells once per month, don't expect to get 1000 months (83 years) of use out of your eneloops.

Cheers
BG

 

[jhellwig]

As a general rule, the higher the state of charge, the faster irreversible capacity fade will occur.

I think this might be more of what I am seeing. It doesn't seam to have affected the lsd ability just capacity.

Running break ins aren't bringing them back either. I realize that over discharging them is bad but as silver fox had described, I saw the gain in capacity and it had no short term effect on the cell.

 

[ryanandty]

I have a question regarding storage and charging of the duraloops as well. I have a maha mh-c808m that I charge them with at half charge (gets them full in 2 hours), and I store the batteries in the fridge inside of a pelican case. Is this similar to anyone else's setup? How long should I expect them to last if I store in this manner and charge or condition them about once every 2 or 3 months.

 

[Battery Guy]

I have a question regarding storage and charging of the duraloops as well. I have a maha mh-c808m that I charge them with at half charge (gets them full in 2 hours), and I store the batteries in the fridge inside of a pelican case. Is this similar to anyone else's setup? How long should I expect them to last if I store in this manner and charge or condition them about once every 2 or 3 months.

A typical rule of thumb for self discharge is that the rate is doubled for every 10 degree C increase in storage temperature.

So if the self discharge for an eneloop at room temperature (let's say 25 degrees C) is 2% per month, then the self discharge rate in your fridge at 5 degrees C will be ~0.5% per month.

Same rule of thumb holds for chemical degradation mechanisms that cause irreversible capacity fade.

So if you want your eneloops to outlive you, charge them to 50% state of charge and store them in your freezer. Never take them out, never cycle them and never use them in any way except to run a "refresh/analyze" step on your C9000 every 10 years or so. I can guarantee that they will stay in tip top shape!

Otherwise, get over it and use the darn things. They ain't that expensive, and they are probably the most robust rechargeable battery ever available to the average consumer.

Quite frankly, I never thought I would see the day when somebody would post a thread wondering what was wrong with their rechargeable battery that was causing it to only have 90-95% of the original capacity after 3 years of use. Wow, how times have changed!

Cheers,
BG

 

[KiwiMark]

I have noticed that some of them are dropping below 1900mAh. Cycling isn't improving them either that much. When they were new they were all close to 2000mAh.

I know that these cells are 07 vintage

dropping below 1900mAh, as in dropping below 95% of what they were 3 years ago? I thought the shelf life of NiMH cells was around 5 years, but at the rate yours are going they will probably still hold over 75% of their original capacity when they are 10 years old. Unless some sort of chemical breakdown happens faster as they get older, of course.

I thought that Eneloops were good, now thanks to this info I think they are EXCELLENT! I already have a dozen Eneloops and about 8 (I think) Imedions. I think that I'll be happy to buy more Eneloops whenever I need to.

 

[Backpacker Light]

So if you want your eneloops to outlive you, charge them to 50% state of charge and store them in your freezer. Never take them out, never cycle them and never use them in any way except to run a "refresh/analyze" step on your C9000 every 10 years or so. I can guarantee that they will stay in tip top shape!

Otherwise, get over it and use the darn things. They ain't that expensive, and they are probably the most robust rechargeable battery ever available to the average consumer.

Quite frankly, I never thought I would see the day when somebody would post a thread wondering what was wrong with their rechargeable battery that was causing it to only have 90-95% of the original capacity after 3 years of use. Wow, how times have changed!

It is statements like this that prove to me why you are truly the "Battery Guy". Very well said.

The only problem is I believe the average consumer has no idea that this technology even exists. They are not aware of LSD cells and all of their specific advantages. For instance, the largest retailer in America (Walmart) does not even sell Eneloops, and I am noticing it is very difficult to find a Duracell white-top "Duraloop" cell in a Walmart store anymore either. They are really not THAT much more expensive than the junk rechargeables that you see for sale.

I guess a company never wants to sell the perfect product that a consumer never needs to purchase again. You would soon be out of business!

 

[ryanandty]

I was just curious about the conditions in which they should be stored and how often they should be cycled. This is all new greek I'm learning in order to fully enjoy this hobby. Should they be stored in the fridge? Should they undergo conditioning on any type of regular basis? Would doing so help me get the 3 years I want out of the tiny gems that I had to sneak in under my wife's nose because she thinks this is a ridiculous new hobby?

I expect them to eventually conk out, but I was just hoping you guys could tell me I wasn't abusing them.



Edit: My bad, I didn't see the meander in Battery Guy's response. Subtleties are hard to catch sometimes :)

 

[45/70]

......I realize that over discharging them is bad but as silver fox had described, I saw the gain in capacity and it had no short term effect on the cell.

This is true, but the gain in capacity doesn't rule out possible long term damage. As I remember, that was also mentioned in that thread.

I ran a break in cycle on 20 of my eneloop cells a couple months ago and they all came out 1890-1920mAh, if I remember correctly. These cells are dated 8/06 and I've had them about two years, so your cells are doing fine, I'd say. No worse for the wear, anyway.:)

What's the threshold? My Quark AA shuts off when the cell voltage is 0.8v (I think...maybe it's 0.9v). Is that too low?

Under load 0.8-0.9 Volt is the recommended minimum voltage. Part of the reason for this, is taking into consideration cells that are used in series applications. In single cell applications, it is permissible to allow the voltage to go lower, provided the rested OC voltage of the cell recovers to 1.2 Volt, or higher.

At rest, OC cell voltage should be above 1.0 Volt and preferably ~1.2 Volts. With the advent of LSD cells and general improvements in NiMH technology, the minimum under load voltage and rested OC voltage may change. We'll see. Also, Keep in mind that continually pushing cells to the lower discharge limit, whether they are LSD cells or not, accelerates cell degradation.

A typical rule of thumb for self discharge is that the rate is doubled for every 10 degree C increase in storage temperature.

Doesn't this apply only to typical operating temperatures? As far as I know, the preservation effect diminishes at some point. For example, comparing cell degradation storing one cell at 5C, and one at 15C will not make as much difference as storing one cell at 25C and another at 35C.

So if you want your eneloops to outlive you, charge them to 50% state of charge and store them in your freezer.

This is the first time I've heard this. I've always been told that it is not recommended to store NiMH cells in the freezer. Is this something new? I know with Li-Ion technology for example, that in some LiCo cells, the lattice structure in the cell can be damaged at temperatures below ~4F (-16C). Is there not a similar effect with NiMH cells?

Also, I've always understood that the best SOC for storing NiMH cells, is basically in a discharged state, eg. ~1.20 Volt. As self discharge is the main cause of voltage depression, due to large crystal formation, this makes sense to me.

I realize that probably the most important feature of LSD cells, is that they have very limited self discharge, but it hasn't been entirely eliminated. Or is it that they do not suffer from voltage depression, as standard NiMH cells do, and only suffer capacity loss?

Sorry for all the questions, but some of your statements contradict what I have learned over the years. You may very well be right, things do change. :)

Dave

 

[MarioJP]

Unless you are using that 15min battery toaster from energizer I wouldn't even worry about it. Just store them and use them when needed. All I have to say is that I never seen a rechareable battery market today that can tolerate soo much.

these duraloops/eneloops are very stubborn to fail (are you listening powegenix and taking notes). Its been more than a year with these cells and have been through real world conditions, especially constant use. These cells get used a lot. Its been borrowed when I have cousins over ,charged in different chargers, including chargers that would mysteriously heat the cells to the point too hot to touch them and one time I heard it hissing. And that is a big no and stop using those battery cookers. Don't think it was overcharging after an hour of putting the cells. It just simply got too hot from the external heat. Also been over discharged that I lost count.

Probably slight overcharge since the voltage would be around 1.55v before terminating.

After all this that thes cells went through put through tests of their capacities. results are that I have yet to see any capacity lost. In fact it exceeds the label capacity on all 8 duraloops.

Now that is what I call durable batteries.

I also want to mention that I am taking silverfox's tip. After cells been fully discharged, put them in a battery holder 4 at a time indivually and short circuit and leave them for 2 hours shorted.

Cheers and happy read lol.

 

[fishinfool]

Enloops cost what, about $2.50 each? If you spend just one hour pondering the loss of 5% capacity of four Enloops after three years, your time isn't worth more than ten dollars per hour.

My time is worth $250/hr. Somebody owes me $7.35 for reading this thread.:wave:

The check is in the mail. :devil:

 

[ama230]

Enloops cost what, about $2.50 each? If you spend just one hour pondering the loss of 5% capacity of four Enloops after three years, your time isn't worth more than ten dollars per hour.

My time is worth $250/hr. Somebody owes me $7.35 for reading this thread.:wave:

We don't take kindly to you Richers around here!!!:devil:

 

[Battery Guy]

Doesn't this apply only to typical operating temperatures? As far as I know, the preservation effect diminishes at some point. For example, comparing cell degradation storing one cell at 5C, and one at 15C will not make as much difference as storing one cell at 25C and another at 35C.

This rule of thumb applies up to most NiMH cells between about -10 degrees C and 50 degrees C. However, it is only a rule of thumb, and should only be used to make gross estimates.

This is the first time I've heard this. I've always been told that it is not recommended to store NiMH cells in the freezer. Is this something new? I know with Li-Ion technology for example, that in some LiCo cells, the lattice structure in the cell can be damaged at temperatures below ~4F (-16C). Is there not a similar effect with NiMH cells?

I have done a lot of detailed temperature cycling tests on lithium-ion cells to much lower temperatures, less than -65 degrees C where the electrolyte is completely frozen. While we expected to see a degradation from this type of temperature cycling, we never have. We have done this on several lithium-ion cell chemistries, including LiCo. To my knowledge, there are no phase transformations that occur in LiCoO2 or other cathode materials at these temperatures.

With respect to NiMH, I don't see a problem storing NiMH in a freezer, as long as you don't actually freeze the electrolyte. I don't know off the top of my head what temperature the electrolyte begins to freeze at, but it should be lower than the typical freezer will go.

The one problem with getting any battery very cold is that the plastic seals may become hard and brittle, or could shrink substantially because the coefficient of thermal expansion is much higher for plastics than metals. The result is that some batteries may leak when stored or cycled to low temperature extremes.

Also, I've always understood that the best SOC for storing NiMH cells, is basically in a discharged state, eg. ~1.20 Volt. As self discharge is the main cause of voltage depression, due to large crystal formation, this makes sense to me.

I will buy that. As voltage depression is largely reversible with NiMH, I don't think that it matters too much either way.

I realize that probably the most important feature of LSD cells, is that they have very limited self discharge, but it hasn't been entirely eliminated. Or is it that they do not suffer from voltage depression, as standard NiMH cells do, and only suffer capacity loss?

My guess is that eneloops will also suffer from voltage depression, same as normal NiMH cells. However, you can usually reverse this by running a break-in cycle.

Sorry for all the questions, but some of your statements contradict what I have learned over the years. You may very well be right, things do change. :)

Dave

No problem, as long as you realize that my answers may be wrong!

Cheers,
BG

 

[Kestrel]

I just rec'd a NIP & unopened 4-pack of Eneloop AAA's (in a trade) with a package date of August 2006, so these just turned 4 years old.

I don't have an analyzer, but I'd be happy to mail these off to someone here who would run a few R&A cycles and report back on the remaining initial capacity and how much they are able to recover? It would be a nice data point to have.

 

[Battery Guy]

I just looked it up, and a typical electrolyte in an alkaline or NiMH cell will start to freeze below -40 degrees C, and will be completely frozen at approximately -70 degrees C. Since most (if any) home freezers do not go down to these temperatures, there is no worry about freezing the electrolyte in these cells, or expansion, bulging or splitting of cell cans.

Most commercial cells have been tested and passed the IEC 62133 temperature cycling test, which exposes cells to temperature variations ranging from -20 degrees C to +75 degrees C, and requires no leakage in order to pass the test.

Bottom line is as long as you don't actually freeze the electrolyte (which might cause physical damage due to swelling and bulging), you can pretty much keep your cells as cold as you like without causing damage.

Cheers,
BG

 

[45/70]

Most commercial cells have been tested and passed the IEC 62133 temperature cycling test, which exposes cells to temperature variations ranging from -20 degrees C to +75 degrees C, and requires no leakage in order to pass the test.

Well, OK. The IEC testing parameters are definitely extremes though, otherwise it wouldn't be a real test, would it? :) I would not care to subject any of my own cells to any of their testing!

I looked around at some of the NiMH manufacturer's sites and most put the lower temperature extreme for storage at about -4F (-20C, same as the IEC test). I have a separate refrigerator and freezer, so the base temp of my freezer is -20F (-29C). So in my case anyway, I think I'll stick to the fridge for my Li-Ion cells. I don't store NiCd/NiMH cells in the fridge.

I would think storing and subjecting cells, regardless of their chemistry, to extreme temperatures such as encountered in a freezer would not be good for them. I realize most refrigerators with included freezers are probably around 0F, but still..... Regardless of the composition of the electrolyte, the cell's internal components will expand and contract when "freezing and thawing", so I would think it better to keep this to a minimum, if possible. And, as mentioned before, I don't really think there is much advantage per 10C increment at the low end. Storing a cell at -20C as opposed to 5C isn't going to make much difference. The biggest benefit is at higher temperatures. A cell stored at 25C is going to last a lot longer than one stored at 50C.

Bottom line is as long as you don't actually freeze the electrolyte (which might cause physical damage due to swelling and bulging), you can pretty much keep your cells as cold as you like without causing damage.

Last time I checked, only aqueous solutions increase in volume when frozen! That kinda rules out most Li-Ion chemistries anyway. :crackup:

Thanks for your insight, BG. :thumbsup:

Dave

 

[Bones]

I just rec'd a NIP & unopened 4-pack of Eneloop AAA's (in a trade) with a package date of August 2006, so these just turned 4 years old.

I don't have an analyzer, but I'd be happy to mail these off to someone here who would run a few R&A cycles and report back on the remaining initial capacity and how much they are able to recover? It would be a nice data point to have.

Hi Kestrel,

If you're willing to ship them to me, I would be pleased to check them out on my MH-C9000 and return them to you thereafter.

I happen to have 8 AA and 4 AAA Eneloops still sealed in their packaging that are also dated August of 2006. I'm intending to wait until their 5th anniversary in 2011 to analyze 4 of each, but that still leaves me 4 AA cells that I can check out in parallel with your 4 AAA cells.

 

[Kestrel]

If you're willing to ship them to me, I would be pleased to check them out on my MH-C9000 and return them to you thereafter.

I happen to have 8 AA and 4 AAA Eneloops still sealed in their packaging that are also dated August of 2006. I'm intending to wait until their 5th anniversary in 2011 to analyze 4 of each, but that still leaves me 4 AA cells that I can check out in parallel with your 4 AAA cells.

Hey, that sounds like a good idea. Better yet, I'd be happy to wait for the five-year mark on these AAA's - how about I send these to you in a year so that you can check four of your AA's and my four AAA's, leaving you with a duplicate set for your 10-year test or something? :crazy:

Cool idea,