Calculate SOC based on cell voltages?

[mlauss2]

Hello,

I have 3 identical 48V LiIon batteries, each with a jkbms, connected in parallel.
Since PV power has not been nearly enough to fully charge them, their (jkbms-reported) SOC values
have drifted apart widely, ranging between 62% and 18%.
Is it possible to calculate the SOC based on average cell voltage or the bms-reported unit voltage (which is very accurate at the moment)?

For example, in my case (12s LiIon): SOC 100% at ~50V, SOC 0% at 38V.

One of the 3 JKBMS has an older firmware (11.261) where one cannot set the SOC0/100 state cell voltage, and this one seems to calculate the SOC based on cell voltage between UVP-OVP settings and reports a very accurate SOC; the other 2 are newer (11.288) and are wildly inaccurate (55% difference between them although they are configured identically and have identical cell voltages).

Thanks!
Manuel