Different dash cams use different power sources, so it's always worth checking how your new dash cam is powered if you're concerned about draining your car's battery. Some dash cams have internal power, or can easily be charged using external power sources. However, the rest use the cigarette lighter/USB port in your vehicle or need to be hard-wired, meaning they do use your car's battery. If you use the cigarette lighter/USB port to power your dash cam, then leaving it plugged in overnight might drain your car battery, depending on if your vehicle supplies constant power to the ports. Hard-wired dash cams can be set up to switch on with the car ignition in some vehicles to save battery, too. If you were planning on using your new dash cam for security purposes, you might want to consider choosing a dash cam with motion detection and using an external power source to make sure you don't drain your car battery.