This was an install we did for a customer's F33 428i Cabriolet, the setup would be the same for the 430i, 435i, 440i, and M4 Cabrio models. We did the Thinkware Q800 Pro (2K front resolution + 1080P rear resolution) dash cam system along with an iVolt battery pack for this car. The iVolt when paired with the Q800 Pro 2CH should be good for about 14-15 hours in regular motion detection parking mode. It can record for longer if using the Energy Saving Parking Mode feature, however we prefer motion detection as it captures more detail.
For this Cabrio, we installed the rear dash cam on the rear window. This provides the best possible view when the top is up. For drivers in the Pacific Northwest, this is an ideal setup since it rains most of the time and the top will be up whenever the vehicle is parked. Hiding the wires and mounting the camera does take an extra hour worth of labour in this case but the result was well worth it for our customer.
As with any BMW, we highly recommend a battery pack to prevent battery drain issues and ensure the auto start/stop system works perfectly. This will not only extend parking recording time, but also protects the car's battery and warranty.