It depends on both the model of the black box and the car itself. In some cars the cigarette lighter socket power supply is not interrupted when the ignition is switched off so the recording can be performed 24/7. The power is cut off more often, some video-recorders are equipped with a rechargeable battery for this case. In the parking mode ("parking monitoring"), the device wakes up when the impact sensor is triggered, captures this moment and goes back to sleep until the next awakening. This function is most successfully implemented in 70mai Dash Cam Pro, a full charge lasts for about 40 activations.