I'm just thinking outloud....

Note. Connection was tight when I checked a week ago.
After getting back towed home on this recent one, + was tight but I could still ~move it~

If you read the OP, as crazy as it sounds, I replaced the T nut on it, and it would still not clamp tight-tight.
I thought it would was the clamp on the cable itself *compressed*, and not allowing full metal-metal contact.
Loaner Battery swapped and it's tight ! Go figure.

I do suspect that on 2X, it was not a good connection, and did start the car, somehow, the vehicle was running down the battery and it was not taking a charge even though there was a connection....
While stranded waiting for a tow....amp clamp was reading 45+ amps, etc.

It's a pretty straightforward system unless I am missing something.
Starter, Alt. Wiring to the Back to the Battery. Negative in the rear and that sums it up....

I'm stumped and mystified.
Regardless, don't plan to drive until I have a solid plan of action...
Me and my 12V blues