I guess that makes sense but ultimately as soon as the 12v battery goes below a certain voltage it'll cut power to the camera. My thoughts are, IF the internal battery stays fully charged when being powered by the 12v battery while the vehicle is being used, it should last in parking mode/standby for a couple of hours on just the internal battery. That'll be more than enough to cover the car on short parks, such as food shopping, but obviously not if being left all day for work or worse, in an airport carpark during a holiday. If that's true that'll be more than sufficient for my needs.