Recently I've noticed that the coach batteries on our Sprinter 250RBS trailer are not charging when being towed. I left Portland, OR with batteries (2 x 6v golf cart batteries in series) at 1/2 charge and drove about 3 hours. Checked the batteries on arrival and found them still at 1/2 charge. I disconnected the + battery cable at the coach battery and measured about 13.6 volts across the battery cable and the chassis ground on the trailer with the TV running. I don't have an ammeter so am not able to see how much juice is flowing.
Any suggestions for trouble shooting further?
They charge just fine when connected to shore power.
Ron