question

First of all some basic LA firgures, these are presuming a GOOD battery with no cell sulfation or shorted cells

A lead acid AGM GEL Flooded etc are normally 100% full when at rest for min 1 hr and a voltage reading of12.7 to 12.9 volts.

That being said

when a LA battery is being charged it needs to see 14.4 volts for 8 hrs and the charger should drop to float voltage which is around 13.4 to maintain level

The above is a indicative set of numbers meant as a ruff example and depend on the battery manufactures figures of course.

Now on on a solar system (you have not mention that so this may not apply ) the mppts will charge to the absorption for its set period 4 or 8hrs there abouts depending on settings to fill the battery to 100%

then float then over night to the batteries standard voltages the below chart is for a battery at Idle and thus must have no charge or discharge for 1 or more hrs, some batteries maybe .2 volts higher so adjust chart to suit

NOW TO THE BMV Question

set the BMS to show charged at say 14 volts and set the period to say 4 hrs at this point the SOC will flip to 100% (if this is not achieved then there is no reset done)

Its always a good idea to have a reset done as LA batteries are not perfect and every battery is different as well and thus the in and outs of the amps flow is not measured correcty unless Peukerts exponent is 100% correct and you may also have to adjust this to suit your battery.

Thus a reset to a known 100% level is a good starting point

also set the Battery capacity to the correct figure

it will then only reduce if there is a current draw. and a reset to 100% happens when it is at a 100% level