That only means the batteries were low, they had self discharged.. When you changed from six to 12 volt (Generally a bad idea) are you sure you wired them properly?
One possible issue.. Many coaches have a device called an automatic generator start.. ON SOME coaches the generator starts off the chassis battery (usually a single 12 volt battery) on others off the house (Which may a six volt pair (NOTE: this pair *IS* a 12 volt battery) or one or more 12 volt batteries.. IF the AGS senses low voltage, it starts the generator.
Home is where I park it!