Just quoting the Owner's manual. Section CH-30. When plugged to charger, 12 volt battery charges after Li-Ion is full, if necessary. Take it up with Nissan, not me.
And yes, accessories most certainly do run off of 12 volt, Section EV-2. Again, owner's manual. Li-Ion recharges 12 volt...
I wouldn't bother. There's a problem with charging to 80%, actually two problems. One, 12 volt battery charges after Li-Ion battery is full, so if you don't charge to 100%+ then the 12 volt battery is working exclusively off of the Li-Ion, and the 12 volt runs accessories (AC/Heat etc.). Two...