[size= 16px]I learned a lesson the hard way and I want to share my experience and also ask a question so I don't make the same mistake again. I have a 2017 Honda Civic and yesterday morning I went out to start my car and got nothing but clicking sounds. Completely dead battery. I got a jump start from a neighbor and the car has been fine since. I couldn't figure out what caused it because I didn't leave my headlights on or anything obvious. Then I realized that the night before, I had left my phone charger cable plugged into the USB port, but my phone wasn't connected to it. Just the cable was plugged in with nothing on the other end. A friend told me that some cars keep power going to the USB ports even when the engine is off and the key is removed, and that an empty charger cable can still draw a small amount of power. He said I should Learn more here about battery drain to understand what happened. Is that really true? Can an empty charging cable with no phone attached actually drain a car battery overnight? How much power could it possibly use? It seems crazy to me that something so small could kill a battery. But maybe my battery was already weak and the charger cable was just the last straw. The battery is about two years old, so it might have been near the end anyway. Does leaving a phone charger plugged into the 12V cigarette lighter outlet drain the battery the same way as the USB port? What about those Bluetooth adapters that plug into the USB port for music – do those drain the battery too? I want to be careful in the future. Should I unplug everything from my car every time I park, even chargers with no phone attached? What about things like dash cams – do those drain the battery if left plugged in overnight? I don't want to get stranded again but I also don't want to be paranoid about every little thing. Please share your knowledge about what actually drains a car battery when the engine is off and what doesn't matter. Any advice for a beginner would be really appreciated because I clearly don't understand my car's electrical system as well as I thought I did. I just want to avoid another dead battery without going crazy unplugging everything every time I park.[/size]