Person plugging the Anker New Nylon USB-C cable into a phone
Justin Duino / How-To Geek
Everything that requires power in your vehicle uses gas. A car charger draws around 4.5 Watts. While the charger is drawing this much power, you'll get about 0.03 MPG less from your car.

Charging your phone in your car while driving is a pretty common thing to do, especially if you’re using it for GPS navigation on a long road trip. Is that charging having an impact on your gas mileage?

It’s common knowledge that running the air conditioning in your vehicle has a negative impact on MPG. That’s why it’s better to open the windows at certain speeds. People don’t typically think of charging electronics in the same way, but should we?

RELATED: Which Uses More Gas: Open Windows or AC?

Where Does the Power Come From?

Whether your car runs on gasoline or electricity, you should think of it as a giant battery with finite energy. Everything that happens in your car uses a little bit of that energy. Whether it’s something as big as air conditioning or as small as turn signals, that energy has to come from somewhere.

Charging your phone when the car is off will take power from the car battery. When the car is running, the car battery is kept charged by the alternator. Your phone still takes power from the car battery when the car is running, but now the alternator is working to keep the car battery topped off.

The alternator gets its power from gas. So while your phone is technically being charged from the car battery, it’s indirectly being charged from the alternator, which needs gas. The fact that your vehicle keeps the car battery charged while driving doesn’t mean you’re making free energy for your phone.

RELATED: How Does an EV Battery's Charge Compare to a Tank of Gas?

How Much Gas Does Charging My Phone Use?

We know that charging a phone in the car (while driving) uses gas, but how much? You’ll be happy to know it’s an almost insignificant amount.

According to a report from Bloomberg, an average car charger draws about 5V at 900mA. That comes out to 4.5 Watts. That’s how much electricity is being taken from the car battery, and replenished by the alternator—which is powered by gas.

Now, a lot of different factors play into gas mileage—type of vehicle, speed, wind resistance, etc. The impact isn’t going to be the same for every vehicle. That being said, according to the report, a typical car charger eats about 0.03 miles per gallon.

Of course, charging more than one phone at a time will eat up even more, but that’s the baseline. Let’s say your car gets around 32 MPG. Even if you charge your phone all the time when driving, it’s now equivalent to if your car got 31.97 MPG.

That’s the moral of the story. Yes, charging your phone does require gas, and that does have an impact on your gas mileage. However, it’s such a small amount, it’s really not something to worry about. Go ahead and use a car charger.

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Profile Photo for Joe Fedewa Joe Fedewa
Joe Fedewa is a Staff Writer at How-To Geek. He has been covering consumer technology for over a decade and previously worked as Managing Editor at XDA-Developers. Joe loves all things technology and is also an avid DIYer at heart. He has written thousands of articles, hundreds of tutorials, and dozens of reviews.
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