Sorry for the incredibly delayed response. I need to figure out how to get notified for posts.
I am not connecting to the HV. I ran 4awg wire from the car's 12V battery. The auxillary battery is isolated from the primary 12V battery by the charge controller shown in the photo.
I've installed an auxiliary 12v battery and battery charger in the backseat of my 2017 Leaf SL. The intention is for the auxiliary charger to only run when the DC-DC converter is on. As far as I can tell, the DC-DC converter is on when the car is in one of these states:
Vehicle is on
Vehicle is...