My alternator on my 2007 Discovery with a 330 Cat and Freightliner chassis quit charging when running. The Generator and shore power charges the batteries so I am assuming the alternator is faulty. It...
Look for a diode based isolator - if you have one they are notorious for dieing and causing the symptom you see. You'll need to use a volt meter to check incoming and outgoing voltage. It is almost unheard of for a high quality alt like yours to die that early.