@13_gecko_rubi
On edit:
Yes, It is the two marked with the yellow X's, as you have stated ... One is main battery the other for the ESS battery.
You can actually trickle charge either the main or ESS with them.
From what I have heard so far, it's not simply wired in parallel. Yes, the negatives are both common but the positives go to two different posts (N1 & N2) in the power distribution center. There is module / ESS relay that controls when to use the ESS and when not to use.
N1-Main battery, N-2 ESS battery.
If you want to isolate the positive side disconnect N1 & N2 in the power distribution box.