question

@photon_trap, SOC calculation is based on a number of factors, but vbatt isn't one of them... except in that the shunt is measuring current through itself as a function of voltage differential between its posts, but vbatt is effectively irrelevant to that measurement.

A charging current = higher v at the "loads and chargers" post than the "battery" post, discharging current = the opposite. By measuring the v differential between the two and taking into account the known resistance of the shunt, a very nearly exact count of the amperes traveling through the shunt in either direction is effected, and thus reflected in the SOC calculation.

This is why all loads and all charge sources must be properly connected to the shunt; if the BMV was using vbatt to estimate SOC, then it wouldn't matter so much if a load was connected straight to the battery, but that's not how the calculation is performed, so in reality if you have a load connected straight to the battery, you'll see vbatt dropping without the SOC dropping, because the BMV can't measure what it can't see. The same is true in reverse - a charge source connected straight to the battery will result in higher vbatt, of course, but would not be reflected in the SOC calculation, so you might have full batteries but showing low SOC because the BMV can only perform its SOC calculations based on the current flowing in either direction through the shunt.

Thus, the SOC calculation, regardless of charging or discharging, will be constantly updating. So long as you have correctly programmed the battery Ah capacity, charge voltage, charge efficiency, peukert exponent, and etc into the BMV, then the BMV simply measures the current out through the shunt and subtracts that from your SOC reading and, likewise, measures charge current in through the shunt and adds it to the SOC reading.

It should always be noted that the SOC reading is an estimate only, though -so long as you've correctly programmed the unit to match your system- a very good estimate.