Can you explain how this works exactly? Especially the first step about
"[adding] in the frunk a cable connected to the 12 V battery"
-- how is this connected?
Well, to recharge the 12 Volt battery you need to access to the (+) and (-) terminal plugs of the battery.
But to access the battery you need to remove a battery cover.
I don't know how complicated it would be to remove the cover but I assume that it might not be designed
to just pop up and you may need some tools and remove some clips.
So I was thinking to try to remove the battery cover to access the battery, then I would install the above
extension cable from the battery to the frunk, and put back the battery cover.
So if I'm stranded, it would be easy to recharge the 12 Volt battery, using a portable battery,
especially at night, or in a rainning day, or if someone else like my wife was expereincing this issue.
Also, I would have a 12 Volt plug available in the frunk, allowing using a mini cooler or a 110v converter.
It just that a drained 12 Volt battery seems to be a common issue to many EVs.
However, when it occurs this can be easilly solved if you can recharge the 12 Volt battery.
The 12 V is needed to activate a relay to have the main 400 Volt battery connected to the car engine.
The main battery then can be use to recharge the 12 V battery. Kind of chicken and eggs situation.