dual batteries & dual voltage sensing relays

[Brissieboy]

Hmmmm, I may have got it wrong based upon this…. https://www.multicable.com/resources...ce-awg-to-mm2/

There is a lot of confusion and mis-use with wire gauges and sizes. According to the old standard, 8 SWG is 12.97 mm2, 8 AWG (also B&S) is 8.36 mm2. There is also 8 BWG (not common now) 14.79 mm2.
The only way to be absolutely sure what you have is to measure and count strands and calculate the total cross sectional area.
Then there is the 'automotive' way of referring to size by 3mm, 4mm etc which doesn't appear to directly relate to either wire diameter, copper diameter or cross sectional area.
The best way to purchase electrical wire is to go by copper cross sectional area only and ignore all the rest.