The battery cable from the battery to the inverter do you use 4-0 welding cable or nomal 4-0 coarse wire. I have read somewhere that the welding cable will not meet code.

you can get ul listed battery cable cobra cable makes it and i am shure others do. regular 4/0 would be impossible to fit into the places in the dc boxes we have to get i think. just make shure you get lugs listed for fine stranded cables