Intermittent voltage in the cigarette lighter is when it disappears there after the ignition is turned off,
and not when the car’s systems turn it off due to a voltage drop.
Why are you telling me all this?
I know how the cigarette lighter in OP's car works.
1. If the car's BMS turns off the power to the cigarette lighter/socket due to the operation of the DVR during day trips,
then it's time to check the car's battery and the DVR has nothing to do with it.
2. If the car's BMS turns off the power to the cigarette lighter/socket due to the operation of the DVR during a long stay at night,
then it will be enough to remove the power adapter from the cigarette lighter in the evening, and in the morning when you return it to its place,
the DVR will turn on as it should.