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Making the Grade

Coydon

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Joined
Apr 13, 2023
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51
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Intra-Michigan-Superior woodland forest
I've noticed two themes around cell representation here, first that the 'grading' system is a marketing gimmick lacking any sort of objective standardization, but then that some sellers are selling 'grade B' cells as 'grade A'.

All cells on the market being discussed here are ones that didn't make the EV market standards. But the ones rejected from there are apparently being further divided in grades A and B? Are the various manufacturers consistent within their own production runs in this grading? Is there a key anywhere for how those various manufacturers' grades differ? Is it a question of capacity and/or longevity?
 
There is no such thing as Grade A. It is a meaningless label given by the distributors of said cells.

EVE began marking non-EV rated cells with a "B" in the QR code giving rise to "B" grade cells.

There are "trusted" sellers that are known to sell new cells that do not meet the EV standard but test at high capacity - 95% rated or better.
 
Also another factor in passing capacity test is the C rate of said test. 0.001c vs .1c can skew test results.

Many times these resellers are claiming lower C testing is needed to meet test.

Same with acceptable voltage drop under load, if a cell is “full” and a .25c or .5c load is applied what is the acceptable %voltage drop on the cell terminals.

I could care less if my 280ah cells can deliver 280ah if I can only supply .01c load without voltage tanking.
 
There is no such thing as Grade A. It is a meaningless label given by the distributors of said cells.

EVE began marking non-EV rated cells with a "B" in the QR code giving rise to "B" grade cells.

There are "trusted" sellers that are known to sell new cells that do not meet the EV standard but test at high capacity - 95% rated or better.
Following recent discussions, I've seen that Docan is creating counterfeit QR codes to change the labeling from 'B' to 'A'. Some members here are promoting other sites that are honest and up front about these grades. It seems many of them recognize some value to the categories. I understand that standards lacking third party certification are unreliable, but that isn't the same as "meaningless".

I'm guessing the manufacturers do some kind of sorting among those that drop out of the EV testing, but the problem is a group of hobbyists adopting these over a short time frame lack the data to make a comparative assessment? IE there is no way to verify within these forums what criteria any of the manufacturers use in grading? Do any of the manufacturers share details along those lines?
 
Also another factor in passing capacity test is the C rate of said test. 0.001c vs .1c can skew test results.

Many times these resellers are claiming lower C testing is needed to meet test.

Same with acceptable voltage drop under load, if a cell is “full” and a .25c or .5c load is applied what is the acceptable %voltage drop on the cell terminals.

I could care less if my 280ah cells can deliver 280ah if I can only supply .01c load without voltage tanking.
Does a C rate test give a good indication of expected longevity? I mean I'm guessing applying or drawing excessive current will damage a battery and shorten it's life, but would a battery with a lower C rating give fewer cycles even if it was not overdrawn/charged?
 
Following recent discussions, I've seen that Docan is creating counterfeit QR codes to change the labeling from 'B' to 'A'. Some members here are promoting other sites that are honest and up front about these grades. It seems many of them recognize some value to the categories. I understand that standards lacking third party certification are unreliable, but that isn't the same as "meaningless".

While Docan may engage in a seemingly shady practice, they are still supplying what appear to be quality grade "B" cells.

I'm guessing the manufacturers do some kind of sorting among those that drop out of the EV testing,

Very much so.

but the problem is a group of hobbyists adopting these over a short time frame lack the data to make a comparative assessment? IE there is no way to verify within these forums what criteria any of the manufacturers use in grading?

Other than being able to do the testing per the datasheet:

Capacity
Internal resistance
Self-discharge

The first two are done pretty regularly. The 3rd, rarely. I let my cells rest for 5 months between tests, and they all trounced the 1%/month figure. The worst one lost 1% in 5 months. The other 8 were under 0.3%.

All my cells met the internal resistance requirement.

they all failed to meet capacity by 2-5%.


Do any of the manufacturers share details along those lines?

No. They don't give a shit about us and have zero interest in supporting an infinitesimal market.
 
Reading Docans site (docanpower) I still see “Top Grade“ listed for most EVE cell, not grade A.

I am also in the mindset that I’d much rather be sold a B stamped QR code of a “quality cell” that have smoke blown up my backside. But I’m guessing they fear they’d lose too many sales.

As for trusting a vendor it seems like something maybe good one time may not be good in 6mo, 1yr, or more.
 
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