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Thread: Eneloop Self Discharge study

  1. #1
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    Arrow Eneloop Self Discharge study

    Sanyo started the ball rolling with low self discharge NiMh cells with the introduction of their Eneloop cells. I, along with several others, have been testing these cells for roughly a year now and they seem to be holding up to the manufacturers claims.

    Sanyo claims 2000 mAh for their AA cells, and we are finding that to be very close. Sanyo claims that they can be used right off the shelf, and that also seems to be true. Sanyo also claims a cycle life of 1000 charge/discharge cycles. I would love to be in a position to check this out, but, for now at least, we will just have to believe them on this. The final claim is that they will still have 85% of their initial capacity after 1 year of room temperature storage.

    This is what I found:

    Here is the initial test data on these cells



    You can see that they are very strong performers. I even included the data from the 30 day self discharge for comparison.

    I then took a pair of cells and stored them on a shelf in my house. Data was taken at 0, 30, 90, and 180 days. Here is what that data looks like.



    You can see that the biggest drop in capacity comes in the first 30 days. After that, things settle down. Looking at the numbers we have about 93% of the initial Amp Hours after 30 days and about 91% of the initial Watt Hours for the same time period. At 90 days we have about 88% of the initial Amp Hours and about 85% of the initial Watt Hours. At 180 days we have about 86% of the initial Amp Hours and about 82% of the initial Watt Hours.

    I can easily see how these cells could still have 85% of their initial capacity at the end of a year. I am only going to project out to the year mark because I am going to be using my cells. Someone else can do the 1 year testing…

    I did not note the voltage of the cells at 30 and 90 days, but at 180 days each cell was at 1.313 open circuit resting volts.

    Update: 3/17/08

    I just finished testing a set of 9 cells that I normally use in my Mag85. I set them aside a year ago and just finished testing them. Under a 1 amp load, they came in at 1578 mAh. Initially they came in at 1871 mAh, so you can see that they did not live up to their 85% remaining charge after a year of storage.

    However, 84.34% is pretty close...

    Several people have reported their self discharge test results and they seem to be quite low for normal NiMh cells. A lot of published information has NiMh cells in the 0.5-1% per day self discharge range. I was seeing around 0.7% per day with several brands of cells, based on short term tests of around 30 days. This seems to still be a little high for healthy cells. The problem 2500 mAh cells will completely self discharge in around 10 days so keep in mind that I do not consider those cells “healthy.”

    Here is a graph of NiMh self discharge rates comparing original cell chemistry to the Eneloop cell chemistry.



    The 0.7% per day line is pretty close to what I, and others, have reported, but it seems to be pessimistic at 90 days and beyond.

    The question of the suitability of the Eneloop cells for use in a remote control or other low drain device has often come up. We know that the self discharge rate is faster early on, then it tapers off. I was concerned that there would be little difference between the normal chemistry rate and the Eneloop chemistry rate, initially, and there might be little advantage in using the Eneloop cells in applications like this. This study indicates that even at the 30 day self discharge rate, the Eneloop chemistry is a lot better.

    Ray (Codeman) ran some discharge tests on some Eneloop cells that had been stored for 12 months. The have a manufacturing date indicating that they are 19 months old. You can find his results in this post. Thanks Ray.

    Unfortunately we don't know how much charge they initially had. Sanyo Europe stated that they were putting around a 70% charge into the cells, and we are assuming that this practice is universal, and has been in place since the cells were first introduced.

    MorePower sent me some RayOVac Hybrid cells to check out. Thanks.

    I will be following the same testing proceedure I used for the Eneloop cells.

    Here are the initial test results.



    Here are the results from the self discharge study on the Hybrid cells. I will add data as it becomes available. I am using the same storage and testing conditions as I did with the Eneloop cells. The test results are from a 0.50 Amp test.



    The Hybrid cells are better than normal NiMh cells, but not quite as good as the Sanyo cells.

    Cannesahs picked up some GP ReCyko AA cells for me. Thanks Jyrki.

    The capacity of the battery was not labeled, so I guessed at 2050 mAh. EDIT: They are labeled as 2100 mAh and 2050 mAh minimum. ENDEDIT These are very strong cells. I was surprised that they almost held up over 1.0 volts at 10 amps. I think the voltage of the Eneloop cells is a little higher, but these are very strong cells.

    Here is the initial data.



    It will be interesting to see what their self discharge rate is. Testing in progress...

    Here is some test data from the Eneloop AAA cells.



    And here is the self discharge study on these cells.



    There doesn't seem to be much self discharge between 30 and 90 days. The odd numbers are from slight differences in the cells. I used 4 cells for these tests and rotated them in pairs for the various test periods.

    Update 5/23/2009

    In March of 2006 I ordered and set aside some AAA Eneloop cells. I just got around to needing them and decided to see what they had left in them as far as capacity goes. Over the last three years they have been stored at room temperature.

    They ended up with about 550 mAh left. This is about 74% of their original capacity...

    Not too bad...

    Tom
    Last edited by SilverFox; 05-23-2009 at 06:50 PM.
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

  2. #2
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    Default Re: Eneloop Self Discharge study

    Hello Silverfox.

    Thx a lot for your time and effort to do this and all the other tests for us here at CPF.

    I just ordered some more Eneloop cells

    Useful information as always, thanks again

    Anders

  3. #3

    Default Re: Eneloop Self Discharge study

    Thanks for all the hard work Tom! I think it's time to start swapping out cells in my hotwire lights.
    Ray
    Good people need to be there for each other. It's the only way to stay sane in a sometimes insane world.

  4. #4
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    Default Re: Eneloop Self Discharge study

    I have 4 Ray-O-Vac Hybrid cells and 4 Eneloop cels that I did a "Refresh-Analyze" on the MAHA c-9000. I plan to let them sit for 30 days (end of the month) and do a discharge test on them. It will be interesting to see if the Eneloops match your results, and how the Hybrids compare over that period.

  5. #5

    Default Re: Eneloop Self Discharge study

    Great work! But some of us consider it fun using our chargers more often!
    Stanley 5 Watt LED spotlights, Streamlight ProPolymer Luxeon, Panasonic Bq-390 chargers, Maha chargers, Eneloops

  6. #6
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    Default Re: Eneloop Self Discharge study

    Thanks for all the work, Tom. That's great info to have, very useful.

  7. #7

    Default Re: Eneloop Self Discharge study

    Forgot to ask, not sure if you know or not how the eneloops handle fast charging with the Energizer 15 minute charger?
    Stanley 5 Watt LED spotlights, Streamlight ProPolymer Luxeon, Panasonic Bq-390 chargers, Maha chargers, Eneloops

  8. #8

    Default Re: Eneloop Self Discharge study

    Yes, this is really great information. Thanks for taking the time to complete this study

  9. #9

    Default Re: Eneloop Self Discharge study

    Great info SilverFox! Thanks for doing this!

    Nick

  10. #10
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    Default Re: Eneloop Self Discharge study

    I think Tom mentioned in another thread that they work fine with the 15 minute chargers, but those chargers do take a toll on the overall life of the batteries.

    Quote Originally Posted by Robstorch
    Forgot to ask, not sure if you know or not how the eneloops handle fast charging with the Energizer 15 minute charger?

  11. #11

    Default Re: Eneloop Self Discharge study

    Nice to see, I wonder how the Rayovac Hybrids compare.

  12. #12
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    Default Re: Eneloop Self Discharge study

    I sure would like to see a heads-up comparision between the Eneloops and Rayovac Hybrids. Hopefully, they will be close to the same, since I loaded up with Hybrids for $3.87 per package of 4-AAs and I used up all 10 of my $5.00 off coupons.

  13. #13
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    Default Re: Eneloop Self Discharge study

    Fantastic work and great news! I am more than happy with this rate of charge retention. Knowing I can count on 86% of a full charge after 6 months is terrific; it takes all of the mental overhead out when trying to remember (or worse, write down) when specific cells were last charged. If you just assume you have around 1.7Ah or so to play with regardless of when they were charged, you'll be in the ball park for your calculated runtimes. Not too shabby.
    The Phaser: A nice EDC with great throw; heat and runtime can be issues.

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  14. #14
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    Default Re: Eneloop Self Discharge study

    I think that a lot of CPFs will now buy a lot of eneloops - and tell others to buy them.
    Its just a shame that Sanyo will never reward Silverfox for massivly upping their sales.
    Still at least we appreciate the work done.
    We call them torches here in England...

  15. #15
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    Default Re: Eneloop Self Discharge study

    It'd be nice to get a comparison of all the major low self-discharge NiMh batteries, but SilverFox is probably tired of super long-term self-discharge testing about now. Maybe if people would donate the the batteries to him, we could persuade him to do another round of testing.

  16. #16
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    Default Re: Eneloop Self Discharge study

    Tom,
    Thank you for all your imformation!! Thank you for all your hard work also.
    Dan

  17. #17

    Default Re: Eneloop Self Discharge study

    Great work !

    So are the Sanyo 2000mah Eneloop's mah better than the Uniross 2100 mah Hybrio's ??

  18. #18

    Default Re: Eneloop Self Discharge study

    Interesting. So they discharge slower, much slower than conventional Ni-MH.

    Question: Given the lower 2,000 MaH capacity, does it mean one will get more recharge cycles than the higher capacity 2700 MaH cells?

  19. #19
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    Default Re: Eneloop Self Discharge study

    hello Etc,

    Sanyo advertises 1000 cycles, without specifics...

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

  20. #20

    Default Re: Eneloop Self Discharge study

    Quote Originally Posted by etc
    Interesting. So they discharge slower, much slower than conventional Ni-MH.

    Question: Given the lower 2,000 MaH capacity, does it mean one will get more recharge cycles than the higher capacity 2700 MaH cells?

    They self-discharge slower to be correct. And yes they should last for more cycles, fewer charge cycles is one of the tradeoff's of the higher mAH batteries.

    I've bought a few and have had a set in our digicam for a couple weeks now which is so far better than regular NiMH's which would self trigger the low battery after a couple weeks.

  21. #21
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    Default Re: Eneloop Self Discharge study

    Quote Originally Posted by Eugene
    They self-discharge slower to be correct. And yes they should last for more cycles, fewer charge cycles is one of the tradeoff's of the higher mAH batteries.
    Especially when one factors in the additional charge cycles *necessitated by self-discharge* that the Eneloops won't need.

  22. #22

    Default Re: Eneloop Self Discharge study

    Silverfox Well Done !!

    Thank you for yr in-depth study of the eneloop, really open my eyes ....

    i will be using the eneloop for my upcoming magmod .....

    as its hard to source for high discharge nimh which is "cheap" like eneloop as compare to R/C sub C batteries in Singapore ....

  23. #23
    Flashaholic* Phaserburn's Avatar
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    Default Re: Eneloop Self Discharge study

    Quote Originally Posted by Canuke
    Especially when one factors in the additional charge cycles *necessitated by self-discharge* that the Eneloops won't need.
    Very good point. I as many cycles are put on a cell because of self-discharge as actual use.
    The Phaser: A nice EDC with great throw; heat and runtime can be issues.

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  24. #24
    Flashaholic* MrAl's Avatar
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    Default Re: Eneloop Self Discharge study

    Hello,

    I see 1000 cycles on most of the NiMH cells i see on the web.
    The wording is 1000 cycles to 80 percent capacity.
    If this is really true, these are great batteries!
    I have by doubts though, but i wont say anything until i've seen for myself.

    BTW, in my quest for the best batteries, best flashlight, best LEDs, i forgot to
    take the time to say thanks to Tom for all his hard work with the testing of
    the various cells...i know it's not easy because i've done some of it myself and
    it is very time consuming and you have to make sure you get everything right or
    the results will not be valid, so thanks very much Tom for taking the time to
    do this, which benefits all of us who care about our lights and cells.
    Take care,
    Al
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  25. #25
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    Default Re: Eneloop Self Discharge study

    Hello Al,

    Cycle life is defined as the number of cycles it takes to get to 80% of initial capacity utilizing a standard charge of 0.1 C for 16 hours followed by a 5 hour discharge. All of this is done at standard laboratory temperature conditions.

    The Battery Handbook states that NiMh chemistry is good for roughly 500 cycles under these conditions.

    Now, if you only do a partial discharge most of the time, your cycle life can exceed 1000 cycles. Duracell did some studies where they charged cells to 85% of full capacity and cycled the middle 60% of the cells capacity. They got excellent cycle life, in the laboratory.

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

  26. #26

    Default Re: Eneloop Self Discharge study

    I agree with MrAl's quest to have the best batteries.flashlights and led's.He does not mention a desire the have the best charger. Iwomder if he and others would help me out with a list of their " best "or favorite chargers.Particularly for use with Eneloop's

  27. #27
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    Default Re: Eneloop Self Discharge study

    My results after 6 weeks self-discharge:

    Sanyo 2700mha -latest from TD (superlattice alloy EVO) --- 2313
    Eneloop AA --- 1782

    So 2700 still winning overall at 6 weeks. Hmm. Are these latest 2700mah Sanyo's really that good?

    Note: 6 weeks of self-discharge, tested on Maha C9000 at 400ma discharge rate. Storage 72F or lower.

  28. #28

    Default Re: Eneloop Self Discharge study

    A note on capacity: I just acquired a 4-pack of AAA eneloops (thanks to Coppertrail), mfgr date apparently 8/2006. I put one into a 1aaa flashlight (L0P CE) and ran it to exhaustion, then plopped it into my BC900 (initial voltage displayed: 0.86 V) and fully charged it at 200 mA (C/4 nominal). Total charge taken was 850 mAH which I suspect means the actual capacity of this cell is somewhere south of 750 mAH.

    I put a second AAA eneloop in the light and used it for a while, I'd have thought maybe to 50% or so. I then put it in the BC900 and the measured voltage was 1.24V which in my experience with HR-3U AA cells has meant the cell is about ready for a recharge. After a couple hours the cell was at 1.55V and somewhat warm. I thought the BC900 should shut down if the voltage got anywhere near that high. I suspect the BC900 missed termination. Anyway I pulled the cell out and I hope it's not damaged. It's in the light right now and seems to be working ok.

  29. #29

    Default Re: Eneloop Self Discharge study

    Quote Originally Posted by paulr
    A note on capacity: I just acquired a 4-pack of AAA eneloops (thanks to Coppertrail), mfgr date apparently 8/2006. I put one into a 1aaa flashlight (L0P CE) and ran it to exhaustion, then plopped it into my BC900 (initial voltage displayed: 0.86 V) and fully charged it at 200 mA (C/4 nominal). Total charge taken was 850 mAH which I suspect means the actual capacity of this cell is somewhere south of 750 mAH.

    I put a second AAA eneloop in the light and used it for a while, I'd have thought maybe to 50% or so. I then put it in the BC900 and the measured voltage was 1.24V which in my experience with HR-3U AA cells has meant the cell is about ready for a recharge. After a couple hours the cell was at 1.55V and somewhat warm. I thought the BC900 should shut down if the voltage got anywhere near that high. I suspect the BC900 missed termination. Anyway I pulled the cell out and I hope it's not damaged. It's in the light right now and seems to be working ok.
    I've seen AAA cells hit 1.60 V regualrly charging on the BC-900 without missing termination. I doubt your Eneloop missed charge termination although it was probably close to fully charged.

    Mike

  30. #30

    Default Re: Eneloop Self Discharge study

    Hmm, interesting, I'm more used to AA's and I didn't realize AAA's acted differently. Thanks.

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