You need some chunky cable to wire your battery to your inverter, and your inverter to your motor. I plumped for 35mm2 welding wire. Some people go up to 50mm2 but that might have been overkill for this project. Welding wire costs about a third of the stuff that is sold specifically for HV EV projects and as far as I can tell, is pretty similar. Certainly capable of carrying what’s required without turning into tinder. BUT this is for my project: don’t take this as a rule for yours. Do the math, as the Americans would say.

[Update 2020-07-24]I have now ordered my welding wire. I plumped for this stuff from CEF, which seemed to be the best deal. It looks to be supplied by Eland Cables – full spec here.