Most monitors do not compensate for Peurkert effect
Heavy loads such as inverter powered MW or coffee maker
Have a harder/stronger effect on battery capacity than the AmpHrs that are counted/measured by the monitor .
EXAMPLE
Use using 60 amps for 1 minutes, is not the same as using 1amp for 60 minutes, the monitor will count each event as 1 AmpHR, but the physical toll on the batteries is completely different, and with 60 amp load the batteries will have a lower voltage and less capacity than the 1amp load, even though the monitor will display the same SOC in each case
This could be your situation, according to battery voltage you were at 50% SOC, Not 78% indicated by AmpHR count,
3 amps or not, you need to get those batteries up to full, that means 14.4v and under 1 amp rate per 100AmpHR capacity,
0.5 amps per 100 at 14.4 volts is what I use to indicate full charge, the capacity count will indicate 100% before the batteries reach that charge rate, but I charge them until they reach that point, more batteries die from under charging sulphation buildup, than over charging, 400AmpHR bank, I charge until batteries take 2 amps or less at 14.4v
