Question: I’m going to be away for a few days and I just realized I left my phone’s car charger plugged in — will leaving something plugged into my car’s cigarette lighter drain the battery in my car?
Answer:
I’ve got good news for you: the 12-volt power outlet in your car, also known as the cigarette lighter socket, will likely not drain your car battery, even if you have something plugged in continuously.
In the case of a phone charger, ask yourself this question: Could you charge your phone without turning on the car? If you can’t, you’re in the clear because your cigarette lighter socket isn’t live when your car is turned off.
That said, if you are in the minority and your car has that socket energized, there’s another silver lining: Your phone charger doesn’t use much power when it’s not charging anything.
There are many more things in your car that are passively draining your battery even if you shut everything off – your car security system has to be live so that it can trigger the alarm and your car also has to have a receiver active so it can unlock your doors when it receives the signal from your remote.
A battery specialist has quoted that the average passive battery drain is about 85 milliamps, especially in newer cars with more sophisticated electronics. This means that even when your key is in its “off” position, your car could be using about 1 watt of power.
Do car chargers drain the battery when the car is off?
For comparison, an older phone charger can output 5 watts of power, while newer ones go into the double digits like 15 watts and 25 watts or more. Again, those figures are peak output when your phone is plugged in to charge. If there’s nothing to charge, there’s not much power to output, so the only battery drain you’ll experience is how inefficient the charger’s circuitry is.
Of course, if you’ve plugged something more energy-intensive into a live socket, you might find the battery drained.
Does leaving the USB plugged in the car drain the battery?
Some drivers plug their phones into the USB port to access Android Auto or Apple CarPlay. Will leaving that plugged-in discharge your car battery? It goes back to the fundamental question: Does your phone charge when your car is turned off?
Even if your USB port is energized when your car is off, as long as you don’t plug in anything to charge, you won’t see much battery drain from an unplugged cable.
The bottom line
Most cars don’t provide power to the 12V power outlet when the car is off, and as a result, if you Google or search YouTube, you’ll find tutorials on how to make the 12V power outlet live, likely because the driver wants to run an accessory even when the car is off, such as a dashcam.
So, if you have left something plugged into that socket and go away for a few days, there’s not much to worry about because the likelihood of your battery draining from having something plugged in is low.
Xuyun Zeng is a content strategist with a wide-ranging content background including tech, journalism, cars and health care. After graduating with highest honors in journalism, Xuyun led a newspaper to win eight awards, helped start an award-winning film industry podcast and has written over a hundred articles about cars repair, state laws and insurance. Prior to joining Jerry, Xuyun worked as a freelance SEO consultant with a mission to create the best content that will help readers and grow organic traffic.
Giselle Gomez is an editor with over a decade of experience editing content across personal finance, education, travel, and sports. In editing for Jerry, Giselle’s focus is on making sure content is consumer and SEO-friendly and helping readers understand all things car ownership. In prior roles, she worked as a content strategist, syndication editor, and writer. Her work is featured in AP, NerdWallet.com, BestColleges.com, and more. Giselle holds a master’s degree from Arizona State University.
