If your camera is hardwired into your vehicle, it will draw power from your vehicle's main battery to operate in parking mode. When you turn off the vehicle, the camera will enter parking mode and monitor the voltage level of the vehicles battery. If the battery voltage level reaches the low voltage cut-off, as set on the camera, the camera will power down. If the battery is already at the voltage cut-off when the vehicle is turned off, the camera will power down immediately. While in parking mode, the camera will continue to draw power from the vehicle's main battery to monitor and record any events.
The amount of time that the camera can operate in parking mode will vary in every vehicle as there are a number of different variables including but not limited to: battery age, battery capacity, battery type, driving habits, vehicle type, petrol/diesel, alternator, etc.
The main purpose of your vehicle's main battery is to start your vehicle and operate its electronics. Therefore, there must always be enough power in the battery to start the vehicle when needed, with any additional power available for the camera to use in parking mode.
If you have an external battery pack installed, the camera will remain powered on until the battery is drained flat as this is the sole purpose of this battery pack.
Once the camera has powered down, it will no longer be able to record any impacts that might occur while the vehicle is parked until the vehicle is started again. At that point, your vehicle's battery or external battery pack will begin recharging and be able to power the camera while the vehicle is running.