Via the fuse box bah. I have not seen many that connected directly to the car battery though. DIY dekit mine last weekend. Then a freelance jiu hu guy came and installed into another frds VW ride, also via fuse box.Does your sis car have external battery pack?
I think yours don't have the warning because you're using external battery? Also, if your car auto cuts of electrical supply to the cig port, then it doesn't drain the car batt and so no warning.
What they will do for me is to connect the dashcam to my car batt directly instead of the cig port.