rebalance 2-year old 100Ah 16s LFP?

[UltrasoundJelly]

Hey guys, I built a 100Ah 16S LFP battery with an Overkill BS and put it into service 26 months ago in my lawnmower. Top balanced. Tested capacity at start was 101aH using a battery tester a 2-3A load over 32 hours.

Stored in my shed at 50-90F all year round, taken out only to mow. BMS reports 26 cycles. I attempted keep SOC at 40-70% all year when not in use, but I suspect that my shunt has a parasitic load so at least once the SOC dropped to 0 for an unknown length of time (probably a week or two). I charge at 10-11Amps, only to full right before use.

I have just run a capacity test and I'm showing 96.6 Ah with the same load (5.4% loss). I noticed that right after full charge I have an cell max delta of 69mA, posting the BMS cell distribution here.

My questions: would you rebalance? If I do rebalance I'd like to keep the battery built and perhaps top off each cell. Is there a problem keeping the BMS attached and placing a 3.65v charge load to each individual cell?

 

[sunshine_eggo]

My questions: would you rebalance? If I do rebalance I'd like to keep the battery built and perhaps top off each cell. Is there a problem keeping the BMS attached and placing a 3.65v charge load to each individual cell?

No problems, but I would just use a charge to get to 3.65V... more challenging if you use a load...

Those cell voltages indicate zero need to rebalance.

Recommend you avoid trying to charge to only 70% as SoC accuracy will drift notably with intermittent use. Periodically charge to 3.45V/cell with balancing set for above 3.40V/cell and when 20mV difference exists. Disable "balance only when charging"

 

[UltrasoundJelly]

No problems, but I would just use a charge to get to 3.65V... more challenging if you use a load...

Those cell voltages indicate zero need to rebalance.

Recommend you avoid trying to charge to only 70% as SoC accuracy will drift notably with intermittent use. Periodically charge to 3.45V/cell with balancing set for above 3.40V/cell and when 20mV difference exists. Disable "balance only when charging"

Great point on the charge haha. I need to proofread my posts more.

Thanks, I've changed those settings. Weird idiosyncrasy with the Overkill BMS is that it resets the SOC calculator when I change a parameter so I guess need to cycle the battery again to recalibrate it.

 

[sunshine_eggo]

Great point on the charge haha. I need to proofread my posts more.

Thanks, I've changed those settings. Weird idiosyncrasy with the Overkill BMS is that it resets the SOC calculator when I change a parameter so I guess need to cycle the battery again to recalibrate it.

That happens sometimes.

Cycling is not necessary. Hitting the full charge cell voltage to trigger 100% sync is sufficient.