First, let me say that I understand that, for my setup, the Multiplus's calculation of SOC will inherently be incorrect.
(Right now I have my battery bank being charged by both my Mutliplus and occasionally by my SmartSolar MPPT. So the Multiplus cannot see the current being fed to the batteries by the MPPT.)
Still, the SOC calculation was better with the firmware immediately prior to v481 that is now.
And I think it can be "hacked" to do better, as below.
Consider the following two screen shots, taken at two parts of the day.
This first shows the battery voltage is 26.56V and the SOC is 57%.
Now, as the day progressed, with solar charging, the battery voltage has increased to 26.82V. But the SOC has decreased to 31%!
I know that this incorrect SOC calculation is because the Multiplus is (apparently) looking at current only, and has seen 7 to 8 Amps leaving the battery all day, but is not seeing current coming in from my MPPT.
But as I said above, the previous firmware of the Multiplus handled this situation better.
Might I suggest a software hack, that when the battery voltage increases, the SOC calculation be prevented from displaying lower? That would solve the false low SOC reading in this case.