We're a big fan of BMW's here at BlackboxMyCar and one of our vehicles is a 2013 F30 328xi with a dashcam hardwired via multi-safer. The multi-safer is a great option for vehicles that have an auto start/stop feature which turns off the engine at stop lights to reduce fuel consumption as it can be wired solely to a constant powered fuse if timer function isn't needed. For our customers who drive vehicles equipped with start/stop, feel free to contact us in advance to swap out the power magic pro for a multi-safer.
That being said while the multi-safer is a better option for modern start/stop equipped vehicles, it's still not the best. The reason we say that is because modern vehicles (BMW's in particular) have sensitive electronic systems and from time to time error messages can show up due to the battery discharge when the vehicle is off. You may get this warning when you leave your headlights on and get back in your car in the morning and while it isn't necessarily reason for distress it's definitely a bit of a nuisance. It's been cold lately in Vancouver and that does affect the charge of a car's battery, the picture below is of the different warning messages we encountered on our 3-series.
If you already have a multi-safer or power magic pro hardwiring kit, one way to combat this is to set a timer function so that the kit only supplies power for a set period of time after the car is turned off (e.g., 6 hours or 12 hours) which will limit how much of the car's battery the dash cam can drain. Also set the cutoff voltage higher to 12.0 or 12.2V if possible to reduce strain. That being said, by far the best option to protect your vehicle's battery is to use a Cellink Battery B. The latest 2.0 gen Cellink Battery B is charged only on accessory power which means that once your vehicle is tuned off it will no longer drain the car's battery. This will not only eliminate the battery draw from the dashcam as it will only be powered via Cellink Battery Pack, but also run longer than a car's battery would by itself. Most car batteries are only good for about 12 hours before hitting the 12.0V cutoff on a DR650GW-2CH whereas a fully charged Cellink would be good for about double.