Husband thinks charging phone drains car battery

Dear Car Talk:

My wife has a 2010 Chevy Suburban that I had to replace the battery in recently. The old battery was only four and a half years old.

I suspect the cause of the battery's premature demise was because she leaves her phone charging cable plugged in to the power port continuously. I see that the tiny power light to the cable stays on even with the ignition off and the key removed. Could that small power demand weaken the battery even though the vehicle is driven daily? She says that's bunk. What do you say? – Jerry

RAY: We're with her. The average battery lasts about five years. So yours lasted a little less than average.

You bought this Suburban in 2010, so I’m guessing you’re now replacing your second battery. In other words, you’re right on schedule. And the phone charger is irrelevant.

First of all, a phone charger that plugs into a power port typically draws about one amp. And it’ll only draw that one amp if there’s a phone that’s actively being charged. Otherwise, all it’s drawing is enough power to light up that tiny green LED that tells you it’s plugged in. That takes a fraction of an amp.

To give you some perspective on how much power she’s using with her unused charger, it’d be the equivalent of pulling over once a day and leaving the emergency flashers on for 10 seconds.

It’s almost nothing. It would be completely replenished once the car is started again, and it would have a negligible effect on the life of the battery.

Now Jerry, you haven’t actually accused your wife of shortening the life of her battery with this phone charger, have you? I mean, out loud?

Oh, you have? That’s too bad.

Well, you owe her an apology, then. Put your tail between your legs, tell her you were completely wrong, that she did nothing to wear out the battery, and start looking for some gourmet recipes you can cook for her in the next few weeks.

And here’s a tip: Don’t tell her she needs to extinguish the pilot light because it’s wearing out the stove prematurely.

Talking about tires

Dear Car Talk:

I’m a 70-year-old woman with a 2016 BMW 228i xDrive coupe, base model. The current tires are the Continental run flats that came with the car. After 28,000 miles, the front tires are bald. The rears still have some tread, but I need to replace the tires and have a few questions. How do I determine if I have “staggered” tires or not? I assume not, but the guy at the tire store asked. I’ve always liked Michelins, and they have both Y-rated tires and V-rated tires. Which do I need?

Do you still recommend rotating the tires? Some places will do it for free if I go back there regularly. Only front to back, or cross them in an X pattern? Sorry for so many questions! I'm grateful for your reply. – Caren

RAY: I'm tempted to do what my kids do to me, Caren. When I text them a series of questions, they just answer the last one and pretend they never saw the others.

First of all, you’re right that you need four new tires. You have an all-wheel drive car, and in order to avoid doing harm to your center differential, you need four tires that are all the same diameter. Worn-out tires will have a smaller diameter. So you need four new ones now.

How do you know if you have staggered tires? The easiest way is to look at them. On the sidewall, you’ll see the tire’s measurements. The number to look for is the tire’s width. That’s a number given in millimeters like “195” or “225” and you’ll find it inside a string that looks something like “P225/55R18.”

If your rear tires are wider than your front tires, your tires are considered staggered, and you’ll need to buy two wider tires for the rear wheels. But you don’t have staggered tires (we looked it up) on your base model 228i.

The letter (Y, V, etc.) is the tire’s speed rating. And unless you’re a closet Lightning McQueen, Caren, you don’t need to spring for Y- or V-rated tires. Y-rated tires are good up to speeds of 186 mph. V-rated tires are good up to 149 mph.

While there’s no harm in having tires that are rated for a much higher speed than you’ll ever drive, you’ll pay extra for those exotic tires. An H-rated tire (130 mph) will be more than adequate for your purposes. And if you like Michelins, they make very good tires, in our opinion. But you can buy anything that’s the same size as the tires you’re replacing.

Do a little research, though. Check Consumer Reports or Tire Rack and find yourself a highly rated tire in your size rather than just accepting whatever the local tire shop has lying around.

Once you get your new tires, we do recommend rotating them. Especially if it’s free!

Your current front tires wore out faster than your rear tires. That’s typically what happens because front tires do most of the braking and all the steering. But because you have all-wheel drive, you now have to buy four new tires even though only two of your tires are completely shot.

If you rotate your next set back to front every 5,000 or 7,500 miles, they’ll wear out more evenly, and the whole set will last a little longer. And as long as they’re not staggered, you can move them front to back or crisscross them. Let the spirit move you.

Happy motoring, Caren.