Idiots to suggest that. I can't find anyone who has done anything or talked about this one section of wiring. That Is why I am reading as much as I can hoping to get it figured out. We should start a new thread because others may want to learn and I bet this is irritating to the OP.
If you want to go big you could do 2x 2/0 awg which is ~140mm2 aggregate.
3x 2 awg... ?
Should I start a thread under off-grid inverters? How do I tag you? I will start one with the subject being "Growatt 12kw 250V 120A Wiring from battery to inverter"