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What should I do if one New Grade A cell is mismatched?

pactolus

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Jun 12, 2021
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I recently purchased eight Grade A EVE cells, supposedly matched and batched, from one of the highly regarded suppliers on this site. The cells arrived timely, were well packaged, and appeared in good condition. I just got around to testing them with a DMM and found that seven of the eight cells are reading 3.293 volts, but one is reading 3.287 volts.

I’ve reached out to the supplier for assistance but would appreciate opinions on what best practice is and what I should expect from the supplier?

Is this normal and therefore should I just attempt to charge the one cell to 3.293 and then top balance the bank? Ask the vendor for one replacement cell? Ask for an entire replacement set of 8 cells that is actually matched?

Thanks in advance for any advice.
 
Connect the bank in its series configuration and charge to 3.4V/cell. (ie 13.6V for 12V)

Recheck voltages at that point.

If they have converged, you are all done.

If there is still a significant difference, top up/drain cells as required without disassembling the pack.

If you want to capacity test that individual cell, you can discharge the entire pack - the capacity of the weakest cell will be revealed.
 
That can be totally normal. The voltage deviation generally just means one cell is at a slightly different state of charge. Top balance them and check the resting voltages again after. I would bet that the cell is just fine.
 
Connect the bank in its series configuration and charge to 3.4V/cell. (ie 13.6V for 12V)

Recheck voltages at that point.

If they have converged, you are all done.

If there is still a significant difference, top up/drain cells as required without disassembling the pack.

If you want to capacity test that individual cell, you can discharge the entire pack - the capacity of the weakest cell will be revealed.
Thanks, @toms. I think I’m going to try this. I really don’t want to disassemble the pack.

@Bud Martin and @A.Justice, I guess when you put it that way I shouldn’t be too concerned. The fact that all seven other cells were matched to the mV made me concerned by the one outlier.
 
I would connect in series with the BMS and put direct in service. Set the charging to 27.6 and see if you have any cell over-volt issues.
 
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