I can't figure this one out. I've got a 2013 Roadtrek 210 popular with an Onan 2800. It's been sitting through the winter and the house batteries are low. The inverter is slowly charging the batteries and the House batteries are low (10.8V), when I start the generator and let it run the voltage on the batteries drops slowly losing voltage as it runs. I stopped the generator at 9.3v. Any ideas as to why the voltage would drop? Is it just that the batteries are so low?