OK, I think I have solved my problem - sort-of. Thanks for the advice Tim.
When I do your earth test, I get a voltage of 1.5mV or thereabouts, so less than the 0.02V you mentioned.
I took all my measurements from the battery terminals as well as my ABR battery monitor for the tests. The auxillary battery was at 12.7V and the main battery 12.55 when I started and the batteries were separated.
When I started the fridge, the auxillary battery dropped to 12.2V on the ABR monitor, but read 12.4V at the terminals. The main battery dropped to 12.35V on the ABR monitor, but maintained 12.55V at the terminals.
So it seems the issue is with the battery monitor - the main battery is not providing current to the fridge, it just seems the battery monitor is getting affected by something - possibly because the fridge and battery monitor are earthed at the same point..... But I guess I am happy that the batteries are truly separated.
Thanks again
Lucas


 
						
					 
					
					 Originally Posted by irondoc
 Originally Posted by irondoc
					

 
				
				
				
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