Has anyone ever been successful bringing a low cell back to life?

[Lukowski]

Have a 1st gen Jakiper 48v 100aH server rack battery.
Never cycled the battery. I believe it was racieved at 50% charge.
Now after some time the inverter is hooked up and ready to go now it shows a low cell UVP.
It's in the ~300mV range. Asked the manufacturer for a replacement cell, but they say the easiest option is to charge the low cell with a "cell charger"?
Apparently they are going to provide me with such a device.
From what I've learned about LIFEPO4 batteries, after it has gone below 2500mV, it is irrepairable.
1. Why would this happen to an unused cell?
2. Has anyone ever been successful charging a low cell back to operating voltage?

I did confirm the low volt with a multimeter, BTW.

 

[WindWizard]

The cell needs replacement and not just charged.

 

[Steve_S]

Depending on how the cell got there (UVP) and how the rest are, it's likely NOT BAD. We need to see what the other cells voltages are.
Even if a cell goes down to 2.0V it CAN be recovered IF IT WAS GENTLE and not forced down by usage.

General Recovery Instructions:

Charge each LOW cell, one at a time, starting at 3.000V and around 10A and let it slowly take the charge till it cuts off. Rinse repeat for each cell. They should all take it BUT BE GENTLE & POLITE ! Once they all get to 3.000 then parallel the cells and top them in INCREMENTS, I would suggest 0.100V increments. Yes slow, painful, TEDIOUS but if you want to recover them....
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They technically can recover IF they were not frozen or cooked while in a state of discharge, if they have, then do one cell at a time and in a safe box in case it pops & leaks. IF you are lucky, they will recover and maybe you've only lost a percentage of capacity. IF they recover to at least 3.400Vpc, I would run at least 3 good cycles through them (charge/discharge) and then capacity test each cell to ensure the packs integrity, because even if One Cell goes wonky, it will affect the whole pack, as the lowest common denominator rules.
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Once you get the cells up to 3.650 (I would stick to 3.600 myself) and fully saturated (meaning taking <2A) and stop charge current. The cells WILL SETTLE which is perfectly normal & expected behaviour. They will likely drop to about 3.500 from 3.600 within 1 hour or so, give or take a bit. They will usually continue to settle till around the 3.400-3.450 mark where it will slow considerably as the LFP Working Voltage range is 3.000-3.400.
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Once this is done, I would setup the pack temporarily with the BMS and discharge the battery pack to cutoff, then recharge through the BMS till it reaches full at a respectable Amperage. 100AH Cell can typically take a Max of 0.5C or 50A charge rate. 20-40A Charge rate would be as high as I would go "for now" while determining their condition.
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When charging at a higher amperage the cells heat up (normal & expected) and the higher the amps the warmer they get. With ESS cells @ 0.5C it's never crazy ! EV Grade Cells @ 5C Charge Rate = another matter ok. We are dealing with ESS cells here, so staying "in context". You will want to check the cells during Higher Amp charging feel the sides etc, they should be consistent / constant... a Hot Spot = Warning Flag ! You WILL NOT GET THAT with Lo Amp Charging, it has to be at least 0.25C and the temps should be notable within 1/2 hour or so. Be diligent & watchful !

 

[Lukowski]

Good News!
They sent me a 10A 3.65v charger. Let that run on the cell for about 30 min and the voltage level came back up to around 2800mV. For the past week I have been letting the growatt 12kW inverter charge the battery, so far the cell has been a bit below the others but its within 100mV.
Having a hard time getting the growatt to run a full charge cycle on the battery. According to Jakiper, they say to set 56v bulk , and 56v float. My other two batteries are at 100% , and this one with the low cell is at about 75%. I think what I'll do is run them all down over the course of the day and then let the growatt charge back up again.