First, Coolant level is critical on the onan. Next, if you have the Xantax remote panel with auto gen start you may simply have inherited the previous owner's settings for when the generator starts / stops? For instance, it could be set to shut off when batteries reach "float".
Tony & Yolanda / Katie & Spencer (the Doodles)
2011 Fleetwood Revolution 42W (450/1250)
2008 Jeep Grand Cherokee (Diesel) behind