A long shot, try disconnecting the 12v battery at the terminals for a while, (longer is better).
If it isn't a hardware issue, this may be enough to reboot the computers, re-syncing and perhaps resolve the problem.
If you can get hold of a car battery charger and fully charge the battery while it is out, that would lengthen the disconnected state for one, and help the battery condition too.
If it isn't a hardware issue, this may be enough to reboot the computers, re-syncing and perhaps resolve the problem.
If you can get hold of a car battery charger and fully charge the battery while it is out, that would lengthen the disconnected state for one, and help the battery condition too.