One black goes to the frame ground and the other should go to the inverter negative post.
So for the electrically uninformed (me) does it matter the one black cable now goes to one negative terminal and the other goes to the other one? It will be tough to get in there to fix it and I don't want to if I I don't have to.
I have to say, in an otherwise stellar design, someone mst have been hungover when they came up with that battery compartment design. It's already unpleasant to work on them, and the fact that they're slathered in road grime doesn't help. I left the rig for a month plugged in and that was enough to boil the batteries so dry that they took half a gallon of distilled water. We'll, we did spill some but most of it went in the batteries.
And yep, I know I need a new charger with the lithiums....I think I already do anyway. But the light weight and ability to use almost all the capacity of the batteries makes it a better choice.