You mentioned in another topic to trust you because you were an engineer. You never said of what so we kind of assumed at least electronics? The circuit diagram shows that 12V is required to power it. It's not a suggestion, it's 12V for a very good reason. What happens if you only power the circuit with 9V or 8V or less? You don't need to know the exact specs of the devices to know that anything below 12V is going to cause issues. This can happen with a weak 12V battery, it drops voltage across the whole system. I did experiments some years back where I measured how much power it takes to start a Leaf. It's not a lot, but if a 12V battery can't handle +150 watts for a few seconds plus whatever else is running at that time and the voltage drops so fast, what do you expect the other systems to do trying to start up with less than design spec voltage?
Maybe you are right though, we need better documentation? I go through enough dead Leaf batteries that probably sometime in the future I can setup an experiment to show in real-time what happens when you try to start a Leaf on a weak battery, the dash response, the LeafSpy codes, multi-meter readings of the battery and then follow it up with a load test and a capacity test of said bad 12V battery. I can see that it would certainly be useful to help with these type of discussions in the future.