Hi Tullywork,
On my 2018 34J that cable runs to the positive terminal in the inner battery. My batteries are installed backward from yours - the positive terminals are in the back of the bay. When I replaced my batteries I took some colored trailer wiring tape and put a different color on each cable end depending on where it was connected. That and some pictures made it much easier.
Here is a picture of that cable connected to my inner battery positive terminal.