I think it must be a common problem. On my rig, the breaker had been covered up by a red spray (used to prevent battery corrosion) by somebody a little overzealous with a spray can. My circuit diagram was nothing more than a very faded piece of paper pasted to the wall of the battery compartment. It's worthwhile to get in touch with Forest River and have them email a copy of the diagram.
Good luck, keep the batteries charged, check water levels frequently and if you suspect a battery, have someone do a load test on it.