I have t6.1 ocean, I put 2x 314ah lithium batt to replace the original 2x 75ah AGM.
The 2 batteries' positive are connected directly.
The 2 batteries' negative are connected via their own vw original battery monitor module and onto chassis metal each.
So in that case you can not use a single Victron shunt to monitor both battery's combined current unless you use a thick like 4 awg wire parallel connect 2 batteries' negative then you can go into a single shunt.
Otherwise, I just removed the 2x original vw factory battery monitor module as they are useless now and replace them with 2x victron smart shunt.
Why remove the 2x original vw factory battery monitor module?
Because now I have 628ah instead of 150ah of leisure, without changing the central control panel's registered battery capacity, it will charge to full no problem, but when it discharges it will go down very quickly as it's only registering 150ah of capacity rather than 628. So now I just use phone to check the soc and it's accurate
