elektrologisch told me on X that I missed the third charging park outside. And indeed, even in my pictures from November 27 we can see far in the background another Electraline totem. The chargers don't seem to be back to back with the ones inside the perimeter, but probably closer to the entrance of the parking. No idea how many charging spots there are.
On November 2 I parked there to come take pictures on the rest stop, I confirmed this third parking is accessible with no gate, parking is free and limited to 4h like the rest stop. There's a gate to access the main rest stop and toilets on foot.