Could a cigarette lighter USB charger drain my battery?

July 26, 2013 9:14 AM

If something is plugged into the cigarette lighter port of a car while it is off (that is, no key in the ignition), can that thing inadvertently draw power (and possibly drain the battery) especially if it is cheap or faulty? Or does turning the car off remove that possibility entirely?
posted by Feel the beat of the rhythm of the night to Travel & Transportation (9 answers total)

It depends on the car. Some cars turn off power to cigarette lighters when off, some don't. If you want to test your car, use a plug that either lights up when it's getting power, or one that connects to something that tells you when it's charging.
posted by DoubleLune at 9:20 AM on July 26, 2013 [2 favorites]

It depends on the vehicle as well as the device you are plugging into the vehicle. My old 1995 Jeep Cherokee had to get jumpstarted because I left the GPS plugged in overnight. I left the same GPS plugged in overnight with my 1998 Toyota Camry and never had that happen.
posted by oceanjesse at 9:21 AM on July 26, 2013 [1 favorite]

Additionally to DoubleLune and oceanjesse: Lots of cars also have two lighters, one which remains powered when the car is off and one that doesn't, for just this sort of thing.
posted by Cosine at 9:37 AM on July 26, 2013 [1 favorite]

Best answer: I've found, as a general rule, that GM cars, as well as some other domestic brands, keep the ports powered, and that "foreign" (even when assembled in the US) do not.

But to answer your headline question - a plugin USB charger, by itself, shouldn't drain your battery if it's not actively charging anything. The power draw of just the charger would be so small that you'd have to leave your car parked for weeks for it to make any difference. If you have a GPS or something else plugged into it and turned on, then yes, after a day or two it could conceivably drain your car's battery.
posted by trivia genius at 9:53 AM on July 26, 2013

To echo Cosine above and emphasize that you have to check the individual outlet, not just the vehicle, I'll add the following data point: my 2003 Ford Escape has 2 outlets on the front center panel, about 1.5 feet from each other, and 1 stays hot all the time while the other goes cold when the car is off.
posted by stoffer at 10:03 AM on July 26, 2013

trivia genuis's answer holds true for my 2010 Mazda 3. It has two lighter ports (one in the centre console and one on the dash) and neither charge while the vehicle is off.
posted by futureisunwritten at 10:27 AM on July 26, 2013

My 2009 Scion xD does not charge things while the battery is not running.
posted by Lucinda at 11:22 AM on July 26, 2013

My 2010 Ford Fusion leaves both lighters/power outlets on all the time, and the GPS/phone charger/etc have drained its battery on a number of occasions.

I was used to driving a Toyota, on which the lighter outlets switched on and off with the ignition.
posted by Juffo-Wup at 12:56 PM on July 26, 2013

As far as I know, most Asian makes of vehicles have cigarette lighter sockets that turn off and most American makes of vehicles have cigarette lighter sockets that stay on (and I'm not sure about European makes). That's why in Asia 12V car accessories such as dash cameras turn on and off automatically with ignition and do not need to be designed to turn on and off by other means (such as sensing voltage level or using a vibration sensor or whatever).
posted by Dansaman at 9:42 PM on July 26, 2013