The charger arrived from NZ this morning and it works perfectly. My expectation that lifting the charge in the batteries to above 35V would allow the solar charge controllers to throw current into the batteries however just isn’t happening.
Timeline:
June 22 Solar stopped working
June 27 Installed Victron solar chargers which didn’t work
June 29 Returned Victron and ordered Genesun
July 11th Genesun arrive but don’t work so get the mains charger from NZ on its way to me
July 24th Mains charger arrives. I find someone with a multi meter that confirms that both the panels are pushing out plenty of voltage. The batteries are happily accepting charge from the mains charger and providing this energy when I ask for it. Wiring “appears” to be Ok and no different to what I was having success with between Melbourne and Elliot. 2 brand new solar chargers perfectly spec’d for the task required are in place but not sending juice to the batteries …

A month of waiting and frustration is enough for me to accept that I don’t know what is wrong and need professional help in sorting it out. Tomorrow I will head toward Darwin and hope to find someone there that can get to the bottom of what is going on. At least I will be starting this 350km section with a full battery.