Today: What a crazy way to charge a cell phone!

Dear Car Talk

Dear Car Talk | Jun 01, 2008

Dear Tom and Ray:

While on my evening walk, I went past a small SUV with the engine running. On the return leg of my walk, the engine was still running. At the completion of my walk, I went back to check the vehicle. It was still running, so I went up to the house and asked the owner if she knew her engine was running. She was charging her cell phone! Question: How long can a modern passenger car be left idling? How much does it cost in gas? Can a cell phone be charged by using just the battery? Would it be cheaper to get an emergency cell-phone charger battery? And safer? What is the wear and tear on the engine? -- Mike

TOM: Well, we can do the math, Mike. An average car burns about 0.15 gallons of gas an hour while idling. That's 45 cents' worth of gas at $3 a gallon. Plus, in an hour you create three pounds of carbon dioxide and who knows how much nitrous oxide emissions? But we don't need to do all of the math to conclude that this is a wasteful way to charge a cell phone.

RAY: It's like air-conditioning your house down to 30 degrees to keep the ice-cream cold, instead of just putting it back into the freezer.

TOM: I assume the cell-phone owner had lost her home plug-in charger, and was using the car adapter because that was the only way she could charge her phone.

RAY: But what she didn't know was that she didn't have to run the engine. If she had simply plugged the adapter into the power point (formerly called the cigarette lighter) and then turned the key to the appropriate position (on some cars, the power point will work without the key in at all, and on other cars the key needs to be in one of the "on" positions), she could have charged her cell phone using only the car's battery.

TOM: No harm would have come to the battery. Charging a cell phone takes so little energy that it's virtually impossible to run down a healthy car battery by doing that. And the battery would have completely recharged itself the next time she used the car.

RAY: Plus, the added advantage of using the car's battery instead of the engine to recharge your cell phone is that you're less likely to attract the unwanted attention of potential car thieves. Or nosy evening walkers.

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