What are the criteria for a bad LFP cell?

[scpanish]

I am curious as to what would be considered the criteria for cell replacement. Is there a document someone can give me a link to?

In one of my 4 yr old 16S packs there is one cell which, when the battery overall is getting down to my discharge shutoff setpoint (3.10v), drops to about .07v below the other cells. The other cells are still very close in voltage. As charge level goes up, the errant cell once again matches the other 15. These are Eve LF280K, originally well matched from Shenzen Luyuan, with about 250 cycles. There are 3 parallel packs, all rely on the JK BMS for top balancing.

Clearly this cell isn't yet a disaster, but it may be heading there. Does anyone know a trustworthy seller with US stock? Buying just a couple cells from China is a big shipping hit.

 

[upnorthandpersonal]

Can you do a capacity test on that once cell?

 

[scpanish]

Can you do a capacity test on that once cell?

I could, but it would be a pain. I'd have to take the pack out of service, and I don't have any specialized gear to do it...I'd need to make something up for the load.

 

[upnorthandpersonal]

It's pretty hard to tell without a capacity test what the status of the cell is. Within a pack, you always have a weakest cell somewhere - it just depends how 'weak' it really is to be concerned about it.

 

[scpanish]

Thanks. Maybe a summer project. When the long days arrive! This is an off-grid house.
That one cell does seem to be the only one showing such a large deviation at the low end. I'll keep an eye on it.

 

[upnorthandpersonal]

Maybe a summer project. When the long days arrive! This is an off-grid house.

Trust me, I know the feeling