I was about to suggest that John, good call.
Disconnect the rear battery and test those leads - not the battery, but the wires that were attached to it. See what voltage you get there. If you're getting 10.5-11V there, the system is useless. You'll probably find that either the cable is too thin or it's relying on a chassis connection.
Thin wires are the most common cause of voltage drop. They're also dangerous - with less conductor providing a path for the electricity, trying to draw a high current heats the wire up and can heat it up so much it melts or catches fire.
If you remove those wires and don't have any voltage present on them, the Redarc unit isn't working as expected (again, it could be cabling).
Also, test the rear isolated battery - if the battery tests at 10.5V, it's sick and suffering badly every minute it's left like that. I strongly recommend that you find someone with a C-Tek charger and get them to do a recycle charge cycle on it. It will help revive the battery.