All dash cams will require an external power source to power the camera, whether it is to keep the dash cam charged for battery powered operation or for a constantly powered car camera.
Nearly all dash cameras are designed to turn on when they get power and turn off when they lose power. This is so they can be automatically operated by the ignition of your car, so you are not having to turn the dash cam on and off each time you drive.
Dash Cams powered by the cars cigarette adapter
The simplest and most common type of power source for a dash cam is the cigarette adapter on a car. The dash cam will have a power cord, often called a car charging cord which is a wire that plugs into the camera and into the CIG adapter in your car. This will usually turn your dash cam on and off when you start and shut off your car. This is because most cars cigarette adapter port loses its power when the cars ignition is off.
If you’re using a dash cam with your cigarette adapter on a car that shuts the power off to the cigarette port when the ignition is all the way off and the key is out, then no, a dash cam will not drain the battery of your car.
If you are using a dash cam that’s plugged into a cigarette adapter port that has “always on” power and does not lose power when your car is fully off, then yes, the dash camera will continue to run as long as it has a source of power and will ultimately drain your car battery.
Dash Cams powered by a hard wire kit
If you are using a basic hardwire kit that only uses 2 wires, typically a red (for power) and black (for ground), this will usually be plugged into a fuse that turns on and off with your car, like an accessories fuse or cig adapter fuse. This will not drain your car battery, as this will not provide power to the dash cam when your car is off.
Using a hard wire kit for parking mode features MIGHT drain your car battery depending on how it is setup.
With a hard wire kit that is made for a dash cam using parking mode, it will usually have 3 wires, red (constant power), yellow (car battery power) and black (ground). This setup is used to be able to use the car battery while in parking mode, so if it detects motion or an impact the dash cam can start to record video. If the dash cam or hardwire kit is not monitoring the car battery voltage, yes, it can drain your car battery.
Even if your dash cam does not fully drain your car battery, preventing you from starting your car, it’s still not good on your car battery to constantly be draining it and recharging it on a regular basis.