Our customer wanted to install Thinkware's Q800 Pro 2CH dash camera on their M3. With BMW's and most other European cars, the battery drainage warning shows up early on when any electrical accessories are installed. Even though newer vehicle batteries are more resilient, to prevent stress on it, an external battery pack is recommended. The owner opted to get Thinkware's iVolt external battery as well as a result.
The customer wanted the camera to be placed in the centre of the windshield underneath the rear view mirror. Luckily the dash cam is inside the vehicle, so it does not affect the sensors built into the rear view mirror. We installed the battery out of the usable cargo space, underneath the trunk space cover.