Don't Worry About The Fuel Used To Charge Your Phone In The Car

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Are you a tree-killing monster if you charge your cell phone with a USB port in your car? A recent Bloomberg article titled Charging a Smartphone While Driving Isn’t as Free as You Think suggests that maybe you are. I think it’s a bit too extreme. The facts aren’t wrong in the article, but a lot more context is required here.


The article is based on findings from retired General Motors engineering executive Jon Bereisa, who found that:

It’s not just using a handheld phone while driving that’s a menace to society. It turns out that charging it in the car has consequences too.

That’s because phone drawing electricity from a USB port cuts 0.03 miles from each gallon of gasoline in a tank. Across the fleet of vehicles in the U.S., that would mean about 970,000 tons of extra planet-warming carbon dioxide a year...

Also, this:

The estimated extra CO2 created by plugging in one phone in every car in the U.S. would be about the same as that produced by 185,257 passenger vehicles in one year, according to an Environmental Protection Agency website that converts greenhouse gas into real-world equivalents. Put another way, that’s the pollution created by burning 945 million pounds of coal.

First off, the basics of this are probably true. If you plug in a USB device to your car, that device will draw 5V at 900mA, which comes to 4.5 Watts. That electricity has to come from somewhere, and the engine does have to work that much harder to counteract the extra load put on the alternator. Energy is not free, ever.

So, yes, plugging in your phone can drop your MPG by 0.03 miles. No argument there. What I have a problem with is the complete lack of perspective.


Do you ever drive at night? Or during total eclipses? Or in tunnels? In that case, you’re even more of a monster, because turning on your headlights are about 40 Watts each, which is like charging ten iPhones for each headlight. On most cars, that’s two, so driving in the dark has 20 times more effect on your fuel economy than charging your phone. Never mind daytime running lights, or how many new cars have LEDs that run much of the time.

How about A/C? In really hot weather, with the A/C on full blast, you can drop your fuel economy by up to 25 percent. That’s right from the US Dept. of Energy. So if you have a relatively fuel-efficent car getting 32 MPG, you’re losing 8 MPG. That would be the same hit as if you were charging 267 smartphones.


Plus, having your phone on charge in your car can give some mileage and environmental benefits, if you think about it. Most of the time I have my phone charging in my car is because I’m getting directions from it.

As you may know, a phone using its GPS and telling you where to go sucks the battery, so I have it charging. Those 4.5 Watts I use are more than offset by me not driving around for miles looking for a place I can’t quite remember the location of; my GPS-guided trips almost always tend to be more direct, which saves a hell of a lot more gas than 0.03 MPG.


Look, there’s nothing wrong with being aware that energy doesn’t come from nowhere, and that charging anything in your car has a cost in gasoline, pollution, and money.

But phone charging may be the absolute smallest offender of all the innumerable things on a car that take energy, which is why I think you can safely ignore this inane article, and if you’re really worried about it, just coast down a few hills or shave one or two MPH from your speed.


Charging your phone in the car isn’t going to kill the planet. Let’s talk about how much energy those multi-screen Bloomberg Terminals use, now...

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Guys, I got this. Just take a massive dump right before you go on any car trip. Less weight will mean using less gas, so you can offset the energy used by your phone.

Trust me, I’m an engineer.