Is LED in Device Charger Drawing Down the Battery?

Dear Car Talk

Dear Car Talk | Aug 25, 2015

Dear Car Talk:

With all these things we are plugging into our lighter sockets these days -- phone charger, GPS, radar detector, you name it -- we end up with these lighter-socket plugs sitting there all the time with glowing LEDs on them. My question is: Do these LEDs draw enough current to pose a threat to my battery's life? Should I be pulling them out every time I leave the car overnight? I do that now, but it is a pain for sure. What do you think?

-- Alan

Well, a lot of cars will cut off power to the power ports (what we used to call "cigarette lighters") when you turn the car off. So it's not an issue for most people.

If your car is one of those that continues to power the outlet even when the car is off (so the green LED light stays on), then yes, you are using battery power overnight to light that LED.

Fortunately, it takes so little current to light that LED that your battery will power it for ... let me do the math ... between 2,500 and 2,700 years before it's unable to start the car -- an LED that size takes an infinitesimal amount of power. The digital clock in your car takes more power.

Of course, if you leave your car sitting for a month, it's likely that the battery will get drawn down. But that won't be from the LED lights on your charger; it'll be because things like the car's computer and evaporative emissions system draw power even when the car is parked.

Great! Now you're going to stay up nights obsessing about how much power your evaporative emissions system is using!

Actually, if you've got several devices, and it bothers you, another option is to get one of those power-outlet adapters that turns one outlet into several. Then you can pull out that one plug when you leave the car and disable everything.

But even that's not necessary, Alan. So free your mind. Don't worry so much. Try to imagine that you're just providing a nice, little nightlight for all the spiders living in your upholstery. Does that help?

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