Had an ONAN dealer service my 6500 Emerald III gen yesterday. One of the problems is the gen will not charge the chassie batttery when running. Long story short, machanic first said the wireing was all backwards. The gen should run off the coach batteries. When checking further, he found that the Emerald III was capable of charging the chassie battery, but some part of the windings had failed. Easiest soliution(suggested by him) is to get a 3-5 amp trickle charger and charge through the univolt system. Also if you have service, make sure that the commutaters and brushes are checked and serviced. Found out that this had not been done since the gen was new (1989) much to my surprise. 3 years ago, that cost me a burned out voltage regulator which cost in the range of $450. Brushes were hanging up that results in arching that leads to the comutater needing to be honed/polished. Worst thing, when they replaced the regulator the brushes were not checked. This can be determined by looking at the screws that hold the brushes in place. If they still have the orig silicone goop over the heads have someone open up and service them.