Many thanks Dan. Just to add a little further confusion, I've just been reading up on the he charge controller I'm intending to buy and it states the terminal size to be 13mm2. https://www.enfsolar.com/pv/charge-controller-datasheet/191 here's the link. Presumably that means I can't connect a thicker wire than 13mm2. Based on your advice and a little bit more research I've done, I think that to connect the batteries to the controller I would need 16mm2 based on a 50cm run of wire or 25mm2 based on a 1 metre run......or am I missing something?
Cheers
Cheers