afaik, thats pretty much the case. or its supposed to be. The 12v battery fires the relays and runs the 12v system like lights etc. the traction battery has an invertor and refills the 12v. But when its not used for several days it seems to go wonky on occasion. Ive lost 4 batteries. all were fine and next time i went out and were suddenly below 4v and according to rac gadgets, unlikely to charge.
Toyota have had a lot of issues but they are not interested and just say you left it off too long.
God help anyone who goes away for 2 or 3 weeks holiday lol
Current Car: Hyundai Kona Premium EV...2 way 40kg hoist
Last Car: Toyota C-HR Excel Hybrid...4 way 80kg hoist