Sterling Alternator to Battery charger, dead Domestic bank

[Bob666]

Hi!

We have the Sterling Alternator to Battery Charger 80 A. It has two outputs:
Domestic +
Starter +

When putting the multimeter symbol for detecting if connection between point A and B:
I get "0000", not "OL" as expected. This means there is a connection between Sterling outputs Domestic and Starter.




Doesn't make sense as those are to two separate battery banks. There is a common minus in the system. However when charging I get different voltages on the two outputs.


I have emailed Sterling in UK but they don't answer emails.
The Sterling has always been like this. Did I get a faulty unit?


The thing is, the Domestic battery bank has died. It could be of high age (from 2011) or because the Sterling has in effect parallel coupled it with the Starter battery (which is conventional lead-acid). That would be catastrophic. But, should I have noticed? We've been cruising for four months and everything has worked ok, until a few nights ago when the NASA BM-1 Battery Monitor showed 10,5 V in the morning, and 0% charge of Domestic bank, before sun came up and solar panel started charging. Had left a few things on in the night, but should have set us back more than 10-20% in the Domestic bank.



Then did a capacity test of the Domestic bank, separated the four batteries and measured them one by one and determined that one is faulty, and two are not so good. I parallel coupled the three best ones, which is what I got now. Need to purchase four new ones.



It could also be the case that I am measuring a connection between Domestic and Start + outputs, but there is no current flowing, perhaps the Sterling, internally, has some smart system with Schottky diodes etc?


I would REALLY like to know what is going on here.


Cheers