I had a dose of the flashing M&S lights with p1843 canbus error yesterday. The measured battery voltage was 11.5V so the flashing green lights shouldn't be surprising. I charged the battery a bit and it's all good now. The aux battery under the bonnet was at 11.5V too.
I think though, it has highlighted that the alternator is below par. Or I'm expecting too much from it... We drove about 500km with the camper batteries (300Ah lithium) being charged by a couple of 30A Victron Orion DCDC chargers (about 60A), headlights and wipers going the whole time, heater fan on, Engel fridge running, etc. The camper batteries started out at about 15% SOC and were at 95% when we got home. Methinks I should check the alternator or perhaps only run one DCDC charger and moderate the load I'm putting on the alternator.