Newbie Question - Measuring cell "true" capacity - % life remaining - damaging cells by testing - Lii-500 test set

jjan001

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Hello Learned ones!

I'm hoping someone can explain to a newbie some discrepancies I've noted as I rebuild my RV pack. FYI - the front page picture on the facebook group of the same name as this website shows the picture of my first battery build. This 10kwatt 48vdc behemoth battery, coupled with 2200watts of roof mounted solar, were able to run the air conditioning/microwave/fridges/etc on my motorhome 24/7. It worked great but....... it needs improvement.

As far as I can determine, the Lii-500 test range in Normal or Fast Mode ranges from 2.8v to 4.2v.​
1 - How do you measure "True Remaining Capacities" for cells that have voltage cutoffs higher or lower than this range? Some cells range from a cut-off low of 2.75v to a cut-off high of 4.35v.​
2 - I normally discard cells that have less than 80% capacity remaining - if True Remaining Capacity cannot really be measured in all cases with the Lii-500 due to question 1, what do you do in those cases?
3 - With a tester that will discharge a cell to 2.8v - will this damage cells that have a low voltage cutoff of 3.0v?​
Thank you in advance for your assistance.
 

LithiumSolar

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1) I use the Opus BT-C3100. This does not address your question though as it has pre-set limits. After you test thousands of cells, you just learn how cells should test and what indicators point to a bad cell. If you're looking to measure capacity based on what the manufacturer defines in the datasheets, something like an iCharger x6 would help. You can adjust the low and high cutoffs for a variety of chemistries. The MegaCellCharger allows adjustments as well.

2) I've been discarding anything below 85% at this point, based on the results of the Opus - which again, don't fit the exact criteria you're asking about.

3) No, this will not damage the cells. You'll find that as soon as it hits 2.8V an the discharger ends, the cell bounces back well above 3.0V at rest. They don't sit that low unless it's self-discharging or something like that.
 

OffGridInTheCity

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Agree with @mike. Here's some more yak yak to perhaps explain a bit more... :)

>1 - How do you measure "True Remaining Capacities" for cells that have voltage cutoffs higher or lower than this range? Some cells range from a cut-off low of 2.75v to a cut-off high of 4.35v.

On the top end - The lithium-ion chemistry (18650 cells) in general top out at 4.2v - its just a chemistry characteristic of lithium-ion. I would be suspicious of 4.35v claims. As another way to look at it - if you did actually charge up to 4.35v (or even 4.2v) on a regular basis - the cells will age quickly and there is almost no power at the 1st 50mv of the voltage range. Most folks shoot for 4.15v (absolute max) or for long live 4.1 or 4.0 or even 3.9. Also, second hand cells packs, even when healthy, could easily have a 30mv difference - so shooting for 4.15v max might mean some packs at 4.18 and some at 4.15 type of thing.

On the bottom end - 2.8v vs 2.75v is trivial in terms of 'power in the cell'. In fact, most every lithium-ion discharge curve starts dropping off between 3.5 an 3.4v. Anything after 3.4v is very little power.

Back to capacity testing. Running tests (OPUS for example) on lithium-ion between 4.2v hi and 2.8v low is normal. This is perfectly adequate to give you an apple to apples comparison between cells and to distribute them evenly to create packs. A more precise measure is to test the overall battery (once completed) to see its capacity anyway.


>2 - I normally discard cells that have less than 80% capacity remaining - if True Remaining Capacity cannot really be measured in all cases with the Lii-500 due to question 1, what do you do in those cases?

Not meaningful to worry about 2.75v -> 2.8v and 4.35v -> 4.2v. The minimal 'power' in these ranges is probably within the variance of testing 4.2v -> 2.8v on cheaper equipment. It won't matter for the purposes of creating of an overall battery.
 

jjan001

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Thank you everyone for your informative answers. If I sum everything up correctly- the amount of power in the 2.75 to 3.0 range (when measured from 2.8v) and the amount of power between 4.2 and 4.35 is not a significant factor in the overall capacity measurement of a cell - if a cell does not have at least 80% of original capacity between 2.8v and 4.2v, it should be discarded.

The reason for my question is due partially to the following cells I've tested - they all should be discarded according to the information provided.
FYI - These cells have a manufacturer recommended voltage range of 3.0 to 4.35. According to another website, the area between 4.2 and 4.35 contributes to about 8% of the batteries total capacity. I'm not sure this is significant to my application as the overall pack will be held to within 3.1v to 4.1v working range.

Brand / Part number​
Nominal​
Measured​
Internal Resistance​
percentage​
LGABD11865 (ICR18650D1)​
3000​
2187​
63​
72.90%​
LGABD11865 (ICR18650D1)​
3000​
2164​
48​
72.13%​
LGABD11865 (ICR18650D1)​
3000​
2232​
28​
74.40%​
LGABD11865 (ICR18650D1)​
3000​
2255​
21​
75.17%​
LGABD11865 (ICR18650D1)​
3000​
2356​
21​
78.53%​
LGABD11865 (ICR18650D1)​
3000​
2361​
22​
78.70%​
LGABD11865 (ICR18650D1)​
3000​
2248​
26​
74.93%​
LGABD11865 (ICR18650D1)​
3000​
2293​
59​
76.43%​
LGABD11865 (ICR18650D1)​
3000​
2340​
25​
78.00%​
LGABD11865 (ICR18650D1)​
3000​
2395​
15​
79.83%​


Your thoughts?
 

not2bme

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The 80% rule is just a personal rule. It's not a hard rule. The primary reason is not to mix lower degraded cells with newer cells. If you have a cell that's 60% and another cell that's 90% in a pack, then there's a likely chance that the 60% will fail faster than the 90%. A cell doesn't degrade linearly, so at some point, going from 50% to 0% may be quick, while going from 90% to 50% might take years.

If all you have are cells that are between 70-80% and you can build a whole pack with them, then I would consider them a good pack. Just make sure you mark them so you know that these packs must always be grouped together.
 

hbpowerwall

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The 80% rule is just a personal rule. It's not a hard rule. The primary reason is not to mix lower degraded cells with newer cells. If you have a cell that's 60% and another cell that's 90% in a pack, then there's a likely chance that the 60% will fail faster than the 90%. A cell doesn't degrade linearly, so at some point, going from 50% to 0% may be quick, while going from 90% to 50% might take years.

If all you have are cells that are between 70-80% and you can build a whole pack with them, then I would consider them a good pack. Just make sure you mark them so you know that these packs must always be grouped together.
well said
 

OffGridInTheCity

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I shoot for 85%+ but after 1,000(s) of cells I have my collection of 80% left-overs. In fact I had 130 NCR18650As at 80-85% from 2019.

This year, I'm finishing up a batch of RING packs and they have been 57% INR18650D2 and 43% NCR18650A. I've created 1 battery (14s88p) with all INR18650D2(s) and another with all NCR18650As... but there's not enough NCR18650As so I sprinkled the left-over 80%-85% NCR18650As thru-out to make 14s89p in a ration of 9 to 80 - and I 'think' it will be OK. I added 1 extra 80%'er per pack to offset lack of 100% @ 100% I have in the other battery.

In other words, over time you may set aside lower % cells and then (perhaps) sprinkle them among packs later on for various reasons. Can't really say scientifically what the long term affect of 9 to 80 will have at 50% DOD - but it satisfies my 'waste not want not' urge :)
 

higher_wire

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Messages
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Per the LGABD11865 data sheet, minimum rated capacity is 2900mAh and they are expected to test >75% of that after 300 cycles. We use 75% of manufacturers' rating as our cutoff, since that's what many manufacturers use (EVs are typically 70%).

If you take that 8% figure as gospel, then you can effectively de-rate Cmin to 2668mAh (and Cnom = 2760mAh). Your cells all test above 81% of Cmin. Granted, that doesn't take into account the extra 0.2v on the bottom end, but even without de-rating they're all >75%.
 

jjan001

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Hmmm - It would be interesting to put that 8% to a test. It would be informative if someone would run a set of LGABD11865's in an Opus BT-C3100, at the standard 4.2v switch setting and then repeated the test at the 4.35v switch setting. Anyone with the right test set and LGABD11865 cells willing to step up?
 

reg_zz

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New to this subject and have determined how to test battery voltage and drop after two week period to weed out the quick droppers. My next question has to do with capacity ( not Rated) but measured. Do you typically rate the amperage from the voltage( charged) to say a cut off of 3.0 volts? These batteries are for laptops for a Charity( children schools) is Central America.
Guidance appreciated.
 

daromer

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Run them through a simple tester like the Opus and you get the capacity. Its often between 4.2 down to 2.5-2.8 depending on tester. Its often close enough to be able to rate the capacity
 

Redpacket

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New to this subject and have determined how to test battery voltage and drop after two week period to weed out the quick droppers. My next question has to do with capacity ( not Rated) but measured. Do you typically rate the amperage from the voltage( charged) to say a cut off of 3.0 volts? These batteries are for laptops for a Charity( children schools) is Central America.
Guidance appreciated.
Maybe helpful to use one or both of cell testing flow charts here:
https://secondlifestorage.com/index.php?threads/18650-harvesting-flow-charts.9714/
Don't forget to test initial voltage & cell IR before anything else.
 

reg_zz

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Chart super interesting. Thx. Question; most 'good' cells are 3.9 to 4.0v.; even after two weeks; the chart says recylce cells under 4.1V. Does that suggest the 3.9 to 4.0 v cells are not worth using?

"Don't forget to test initial voltage & cell IR before anything else." Does this mean when I open battery pack and disassemble batteries?
 

OffGridInTheCity

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Chart super interesting. Thx. Question; most 'good' cells are 3.9 to 4.0v.; even after two weeks; the chart says recylce cells under 4.1V. Does that suggest the 3.9 to 4.0 v cells are not worth using?
No. A capacity test (of a cell) is typically a top-off-charge + full-discharge + full-charge leaving the cell at top voltage - 4.2v in theory but it drops to 4.17v (or so) immediately as you take it out of the charger. Its these that sit for 2 weeks ... and should stay above 4.1v. If they don't, it means that they are self-discharging and should be tossed.

"Don't forget to test initial voltage & cell IR before anything else." Does this mean when I open battery pack and disassemble batteries?
Its just means as soon as practical because if you test for IR first it can save you significant time as you won't need to spend the hours on the top-off/discharge/charge cycle.
 

reg_zz

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Makes sense; thx Any thoughts is 3.9-3.95 V batteries will work in rated 3(4.2v) battery pack?
 

floydR

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What are your goals?
New to this subject and have determined how to test battery voltage and drop after two week period to weed out the quick droppers. My next question has to do with capacity ( not Rated) but measured. Do you typically rate the amperage from the voltage( charged) to say a cut off of 3.0 volts? These batteries are for laptops for a Charity( children schools) is Central America.
Guidance appreciated.
Are you talking about single 18650's or complete Laptop batteries with typical voltages from 10.8v(3s)to 14.8v(4s)?
I test single 18650's in an Opus BT-C3400, complete laptop batteries are usually tested with a Battery analyzer which can tell you the condition of the batteries. I have heard of people that rebuild batteries. But I suspect that either an external battery with the same voltage as the laptop charger or aftermarket batteries would be best.
often I am confused
 

reg_zz

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The goal are primarily to supply laptop batteries that will last one hour or so. Power in Nicaragua is sporadic especiialy in rural area and these are the areas in which these laptops are used. Free laptops are available from FreeGeek however often the batteries are not working.
 
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