How do the 2 batteries work?

I'm new to PriusChat - just got a 2018 Prius Prime Advanced so I'm pretty excited.

I have a question/concern though:

I plan to purchase this cigarette adapter that can potentially draw up to 75 watts:

If I put my car into accessory mode (press power button without holding the brake), and I use that adapter to charge my laptop, does it draw power from the battery pack in the trunk or the typical car battery from the hood..?

If I'm parked and charging my car (plugged in J1772 and charging), will the Prius Prime be smart enough to route the power from the (big) battery pack in the trunk (while it's charging) to power my laptop?

The worst case scenario that I'm concerned about is:
- I'm parking and charging my car (J1772)
- I switch the car to accessory mode
- I use the cigarette adapter to charge my laptop for 3 hours, for example
- the front battery ends up dead, even though I've been charging the back battery (J1772)
- I've got to call AAA for jumping the battery now, which I've heard is more complicated than jumping a regular car..

Any thoughts?

Some additional misc. notes to consider:
- I'm well aware that I've I'm not charging my car via J1772, I should not switch it to accessory mode - just leave the car READY to drive, and just park - that way, I'm sure the engine will kick in to run the engine to charge the batteries
- Whenever I plugged in (J1772), the car forces the car to turn off, I cannot go into READY mode when charging, so I can only take advantage of accessory mode when plugged into J1772

 

I don't intend to leave a laptop unattended for charging in the car.
I would be in the car - using the laptop - while charging the car (J1772) - while charging the laptop (USB-C cigarette adapter).