In our last three RVs we have left the inverter on all the time. The first 3 didn't have AGS. The current one does. I did have to add batteries to ensure the batteries stayed above 50% DOD. A common mistake is measuring voltage under load. The 12.1 VDC DOD number is based on the battery being at rest i.e. With no load. If the battery is under load then that number is incorrect.