I would argue that 1-2 times per year is completely unnecessary if you engage the BMS in regular passive balancing at the typical > 3.40V/cell, 30-70mA balancing current.
This depends solely on the relative rates of self-discharge. If they are different, they will go out of balance at that rate, regardless of "C" rate.
Correct with context, and it depends on the user. Charging to 95% SoC at lower voltages takes a long ass time: 6 hour absorption @ 3.4V/cell. If running on a generator, someone's going to be pissed.
Nope. User recovered near full capacity by holding at 14.2V for a week. BB won't balance below 14.2V, and the user never engaged balancing over 3 years of use. I don't know the specs, but I suspect the BB passive balancing is more robust than your typical 30-70mA BMS.
The typical audience here:
Those buying low-end battery packages at $400-500/100Ah 12V
Those building DIY batteries from gray market cells.
Cell imbalance that impacts normal use is commonplace.
Having put together a few cheap LFP batteries ( not yet installed in my boat as I’m designing a new BMS. ) my experience is currently with a 3P4S battery configuration. These are cheap cells.
Clearly thd 3P set can’t be individually balanced so the capacity of that group is determined by the average SOC
The overall SOC , is therefore determined by how close each series set is to one another since battery Based charging stops once the upper voltage is reached even if tail current is still high.
But in reality if SOC moves by 10-15% across each 4S at charge stop point what does it matter.
I have big electronic load programmed to simulate my boats discharge profile ( more or less ) typically discharge current rarely don’t exceed 1/10 C and equally charge current don’t exceed 1/5C
After many test cycles I find imbalance ( assuming Inital cell balance ) is less then 5% different from the original point.
It’s so small that I’m not bothering with balancers in the BMS.
I do know that high C , ie 0.5 -2C does tend to create imbalances. But this is not my scranario.
My results tally with early adopters with low C usage.
Hence minor imbalances within a series string are of no consequence.
I would not accept a battery that found itself with 50 % SOC difference whilst under the sand charging patterns as it’s neighbours. Those types of cells don’t belong in that bank.
