Results of Capacity Testing 18650s for 1,600+ Cycles

Overmind

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@Wolf Thanks, I'll 1st check if e-bay UK has any offers since I do have friends in the UK that come back home from time to time.
 

Generic

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Ok, it is time to release the next set of results. Finally seeing some degradation! Here's the chart:

image_mntqhg.jpg

And a little closer look:

image_lxgtfw.jpg


You can see a definite trend. Just going to repeat a few things if you don't want to read from the beginning. Since I am rotating cells every 25 cycles, and the right two slots get warmer than the left two slots, when a cell is on the right side, it benefits from heat adding capacity, and when it goes from slot 4 to slot 1, the capacity takes a hit. Also, the missing data for the THLD cell in Cycle 129 is from the slot being sticky and going null on the recharge. I didn't get a reading, but when I took the cell out and put it back in, it was at 3.29V, so I know it had gone through a full cycle. Also, because I am rotating every 25 cycles, I wait until 5 cycles into the next rotation to compare to the first 5 cycles, so that there is no slot selection effect.

With that being said, here is the degradation observed over 205 cycles. The first row is the average of Cycles 1-5 and the second row is the average of Cycles 201-205 for each cell. The third row shows the percentage of degradation of eachcell.


image_aphvrs.jpg


Please keep in mind that the LG cell did not start out this test as a new cell, and already had a number of cycles or cycle equivalents on it before the test got started. The other cells are 8 year old cells that were never used. And as most of usknow, degradation is not linear, it accelerates.

Anyway, I'm continuing this test. I just finished Cycle 213. I would have posted this earlier, but I didn't really have a chance.
 

Wolf

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@Dallski,

Nice work on graphing those results. I had similar results with the "do green sony cells suck" experiment although I only did 11 cycles.
I did find out one thing though. If I let the cell rest for a day or so between cycles the results where much more even and consistent.
It's also interesting that every so often the cells jump back up as if they want to do better and then go back down over the next couple of tests.
It would be interesting to see if you let the cells rest a day or two and then test them again if they jump back up like some of my Sony's did.

It's only 11 cycles but it does show the downward trend of the 56 cells.Some of them where pretty flat linethough pretty even all across the 11 cycles. The big A pillar is me playing with the SKYRC and pretty much ruining 4 cells with an 20mA cutoff charge but boy did they have a great discharge result but only once. :)
Wolf

image_hyhgpr.jpg
 

Generic

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Thanks Wolf! You give a lot of effort testing cells and chargers, so it means a lot coming from you since you're kinda in the same boat as me. I wish I could test these at 200mA, only test from 80% to 20%, and give them a break in between and see how much life they could give. But by the time the test was done, lithium would be the new NiCd LOL. I'm trying to put the most stress on these cells that the Opus can give them within reason, of course. Im getting roughly 3 cycles done a day at 1A charge/discharge, and 1 break between night and morning. In real life, these will only do 80/20 max, maybe 200mA on average, and only go through one charge/discharge cycle a day. So whatever results I get, they are kind of a worst case scenario, really. And they are pretty darn good so far. If you get double cycle life by just charging to 4.1 instead of 4.2, imagine what you get if you only go between 3.4 and 3.9! Anyway, there might be a time where I give the cells a break for a couple days, but I dont see it coming up. Maybe when the cells degrade a bit more. Lastly, I know people say there is very little capacity between 4.1 and 4.2V, but as you observed with a 20mA cutoff, you can pack a lot of charge into an older cell between 4.1 and 4.2!
 

Wolf

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Dallski said:
With that being said, here is the degradation observed over 205 cycles. The first row is the average of Cycles 1-5 and the second row is the average of Cycles 201-205 for each cell. The third row shows the percentage of degradation of eachcell.


image_aphvrs.jpg

@Dalslski

Here is another look at the numbers with a little bit different formula. It calculates the percentage of capacity lost over the ~200 cycles and its not that bad.The worst one is the LG and as you said was not a new cell anyway.

Wolf


image_fglnql.jpg
 

Oz18650

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If you have the results for tests 101-105, it would be interesting to me to be able to compare the rate of degradation over time.
Ie. Is it a straight line from test 1-5 to tests 201-205, going through tests 101-105?
OR does the rate of capacity drop increase (or decrease) over time?
Tests at 300, 400 and 500 cycles would really show how this progresses, but it is a lot to ask.
I think this would help people to decide how important SOH (based on current capacity compared to original capacit) is when deciding on using cells.
Some people only use cells with at least 80% of original capacity, while others use a different % of original capacity, while others use "must have at least 2000mah capacity", while others use "must have at least 1200mah capacity".
All of these approaches seem to work, however I don't think there is much info on " How will the resulting packs last over time".
 

Generic

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@Wolf: Technically, you are correct - degradation should be the number you posted, while the number I posted is....something else. I'm just so used to the other way around I didn't think about it. From your calculations, the LG cell lost 5.5% capacity over 200 cycles. According to its data sheet, it is a 300 cycle rated cell, meaning it should have about 80% of its original capacity after 300 cycles. It seems to be outperforming the datasheet numbers for some reason.

@ Oz18650, Yes, check the Original Post, I have been updating that incrementally so that anyone who is new to this forum can get the whole test without sifting through each page. It's fairly straight-line right now, but with so little degradation, it's hard to say. I'm pretty sure that degradation does accelerate with cycles based on the testing I've done with my genuine cells, but it hasn't shown itself in this test, yet.
 

Geek

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Has anyone ever found any datasheets from the manufactures 'generic' cells? Specifically the ASO and SZN batteries, as I do have a reasonable quantity of them.

It looks like they hold up reasonably well, and I do intend to use them. Many came from cheap laptop batteries with BMS problems, so the cells have tested quite well.
 

Overmind

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Just test their capacity and then you could select them for different purposes.
 

Generic

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Geek: One of my motivations for starting this test was the lack of data sheets for these cells. In all of my searching, I couldn't find anything. CJ does have some data sheets for the new versions of their cells, but nothing for the cells I have (2011 - 2014 manufacturing dates).

Sorry for my leave of absence, it says my last login was the 22nd of April. Ouch. Just took a break from this forum and used forum time for other stuff. I did keep this test going. I've now dedicated my Opus to this test for 1/3 of a year now. Wow. Yes, I just finished my 350th cycle! Didn't think I would make it this far, but I'm really glad I did. Here are some results:


image_msdqve.jpg



image_qpdmux.jpg


And here is the degradation (second number is Cycles 301-305)as calculated by the method mentioned by Wolf back in April. Makes more sense to do it this way. Assuming I reach 405 cycles, I will use this same formula.


image_rbbkgc.jpg


It seems the more data I gather, the more questions I have. Like, why am I seeing such small degradation? Is there something wrong with my Opus? With my testing method? For example, the data sheet for the LG cell rates the cell as 80%+ remaining capacity after 300 cycles. The LG cell that I'm using in this test came from a used Laptop pack that had an unknown number of cycles and cycle equivalents. And yet, 350 cycles after an unknown number of previous cycles and like 8 years after the cell was manufactured, the LG cell is still doing great! Oh and the generic cells are not doing bad either. I mean the THLD cell has seen 6% degradation, and Cycles 348-350 were the first times this cell saw less than 2000mAh, but this is like a generic cell that nobody has heard of, unlike a number of people who have CJ or ASO cells. I was expecting 100 cycles before this cell was toast and it's nothing like that. Does anyone know what's going on here?
 

Oz18650

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Thank you for keeping this test going and reporting back here.
There is never very much real information of this type because it takes so much time and effort.
It is great to see real life degradation info.
I think this gives second life storage members hope (and reason to think) that thier cells can last well.
Thank you again.
 

Wolf

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Dallski said:
..............I mean the THLD cell has seen 6% degradation, and Cycles 348-350 were the first times this cell saw less than 2000mAh, but this is like a generic cell that nobody has heard of, unlike a number of people who have CJ or ASO cells. I was expecting 100 cycles before this cell was toast and it's nothing like that. Does anyone know what's going on here?..............

Great test. That took some dedication.

The only thing I can think of is that there are some "cell manufacturers" (how many plant that make 18650s really are there?)that buy class "B" cells from major manufactures. As in slight cosmetic damage likethe print on the wrapper was wrong or it didn't get printed. The wrapper was not shrunk right etc etc.
I mean when you manufacture millions of cells in a high speed environment there is bound to be something that goes wrong on a regular basis.
So to recoup some cost these cells are offered to the aftermarket.
So I'm thinking they buy these cells pennies on the dollar rewrap and sell at a reasonable profit. In essence you are getting a properly manufactured cell with a generic wrap. I'm just guessing of course. But it certainly sounds entrepreneurial for some industriouschinese fellow.

Wolf
 

Generic

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Thanks Oz! I agree! I see a lot of theory and data sheets, but I really haven't seen anyone take the time and effort into actually testing any cells. I guess most forum members should pay attention to how the LG cell does, as most people discard the generics. As for real life, I think the results would be even better, but I'm kind of stress testing these cells to compress the time. There's no way in real life would you do 3 full charges and discharges just about every day at 0.5C and leave cells fully charged every night.

Wolf, that's what I believed at first, but I'm pretty sure these are all non-Japanese and non-Korean cells. These are all probably produced by factories in China, Thailand, Singapore, etc. I have generic cells from 40 different manufacturers and counting. One thing I have noticed is the positive cap. You can usually identify a Japanese or Korean cell from the positive cap depending on if it has 3, 4, 5, or 6 prongs because each manufacturer has its own patent on its number of prongs. I think there are a few main generic manufacturers like CJ and ASO, and then there are more generic generics that rebrand those cells as well, based on similarities to the positive caps.

I know we all think of China as crap and inferior, but you have to remember that these are the same people that are capable of making high quality items like iPhones and stuff. And China blatantly rips off intellectual property from around the world. So it's very possible that you can have an 18650 manufacturer in Shenzen making Samsung copies that are actually good. Just throwing that out there.
 

ozz93666

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Brilliant work Dallski ... this fills in a big gap in our knowledge .... just what sort of life can we expect from generic cells ???

It would seem from your early results that they hold up well , perhaps just as good as recognized brands ... this sounds logical , it's basically the same chemistry...

It's like all things , people don't know what to trust , and so are prepared to pay more for sony for some sort of piece of mind , but it appears there's no need ....

What we want now is to decide on a good supplier ... there's a guy on Youtube who buys from 'Queens' , he does a very professional job of testing capacity ... some cells from Queens , slightly larger than 18650 , sell for 6.5 WHrs/$ including delivery , the best value I've seen.

This is the channel and cell ...https://youtu.be/4jiL9sKleEg
 

Generic

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Hi Ozz, there is more to a cell than just cycle life. I will also be testing for safety in the near future, like seeing if the generics skimp on PTC and CID protection. Seeing the generics perform well is like you mentioned, it's just chemistry. Unlike Lead Acid, most of the cost of lithium ion cells is not the raw materials, but rather the processing of those materials as well as R&D, and assembly. Generic cells are cheaper than brand name cells mostly because the Chinese manufacturers steal all the IP from the big names. It's very similar to why generic drugs are usually so much cheaper than the name brand drugs. And I would break down generics further into (1) name brand generics like the three I'm testing; (2) generic generics like the ones that just say "INR18650 3.7V" or something similar; and junk generics like Ultrafire (rewrapped end-of-life genuine cells) and Trustfire (new cells with 1000mAh or less capacity). You do get peace of mind from buying brand name cells, though. I wouldn't be doing this testing if I knew I had legit Samsung or LG cells.

Also, the video you refer to - that's Thunderheart, a well known member of this forum. You can see his posts here, he is very thorough in his research. He buys from Queen Battery, check his videos for a link.
 

Generic

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Time for an update! Just finished Cycle 405, and here are the usual charts I post. I can see that the CJ cell is starting to accelerate its degradation, but the LG and the ASO are still doing great!


image_zzmjyi.jpg



image_nvdkau.jpg


And here is the degradation chart:


image_fcubqt.jpg


I feel like I really have to go for 505 cycles just because 500 seems to be the magic number that most cells are rated for. Will also probably put together a video with pictures of all the cycles once I hit that mark.

On a side note, I also started safety testing my generic cells. Not the ones used in this longevity test, but other cells from the same manufacturers. I finally learned what PTC does when I was testing for CID. Turns out that when you try to short out a cell, or use it for a higher discharge rate than what it is rated for, you will not trigger CID, but rather PTC. I was getting strange results shorting my cells, but that was the PTC protection working. Spoiler: CJ and ASO have PTC protection. I'll save the rest for another thread in the future. Stay tuned!
 

thunderheart

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Generic said:
why am I seeing such small degradation? Is there something wrong with my Opus? With my testing method?
...
Does anyone know what's going on here?

If you want real numbers - forget about Opus. It always shows higher capacity while discharging only down to 2.8V.
Opus is good for comparative testing and sorting good/bad cells for further use but for scientific work like the one you do it's a crap. I'm not talking about it's steel contacts and their resistance yet...

Plus, when they went from v2.1 to 2.2 (if i'm not mistaken) they updated the firmware to show higher results because people were buying 3400mAh NCR18650Bs, testing them, getting somewhere around 3250mAh and opening claims on AliExpress)))). Opus is not a precise instrument. It's a meter for approximate rating of a cell.

P.S. You did an excellent job, i'm taking my hat off!

P.P.S. Tell me please detailed rules use follow during tests.
 

ozz93666

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thunderheart said:
Generic said:
why am I seeing such small degradation? Is there something wrong with my Opus? With my testing method?
...
Does anyone know what's going on here?

If you want real numbers - forget about Opus. It always shows higher capacity while discharging only down to 2.8V.
Opus is good for comparative testing

I tend to agree , but this is a comparative test .. As long as same procedure was used throughout these are accurate results ...
Contact resistance due to cell not being held firmly won't effect capacity readings significantly , only internal resistance measurements .

We can see results are reliable because LG are consistently lower following a tight line of it's own , if there were errors , results would be jumping and brand lines mixed .

The small inaccuracies in in opus or whatever must be reflected in the small spikes and dips in each line , which don't deviate significantly from each brand line .... I guess if you had 100% accuracy in measurement each brand line would be perfectly smooth .

Very good news to see cells having such a long cycle life.


I think after 500 cycles we have all the data needed , we can see the best performers , and project the graph line forward and have a good idea what capacity will be after 1,000 or 2,000 cycles ....

Just one more thing we need to know ... testing cycle life is normally carried out over a short period of time ... but what if you only cycle 50 times a year ??? Will deterioration from other factors outweigh deterioration from cycling , will old cells 20 years old , still be performing reasonably well if not cycled more than 50 times a year ???
 
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