Intermittent Battery Failure Points to Power Drain

Dear Car Talk

Dear Car Talk | Jan 11, 2018

Dear Car Talk:

We have a 2015 Ford Edge with 14,000 miles, purchased new in January 2016. We have had the battery go dead four times. The first time, Ford service sent a technician to jump-start the car. The second time, the car was towed to Ford and the battery was replaced. The third time, the car was towed and the battery replaced again. And the fourth time, Ford kept it for five days and found no problem with the battery.

Usually, but not always, the battery goes dead when the car sits for three to four days. We are retired, so the car is not driven daily. Any idea what could be the cause of the battery going dead? The car is under warranty, but this is a frustrating problem to have. We enjoy your column. Thanks. -- Cheryl

It sounds like you have a good, old-fashioned power drain, Cheryl, and the dealer needs to figure out what's drawing power while you're sitting on the front porch drinking Cosmopolitans.

The other possibility is that your charging system is not adequately recharging the battery, but I'm going to assume they tested the charging system when they kept your car for five days.

You've got enough miles on the car that we can rule out "very short trips" as the problem. If you drove the car three-quarters of a mile once every four days, the battery might not recharge, but that's clearly not the case.

So, the problem is not with the battery (which they've replaced) or the charging system (which I'm sure they tested). Therefore, something is using the battery while the car is parked.

I don't know about the 2015, but I know that on previous Edges, Ford had problems with the door-latch switch. Now, why might that kill your battery? Well, the door-latch switch tells the computer that the door is completely closed. That, in turn, turns off the dome light.

On lots of modern cars, the dome light stays on for 30 seconds or so and then fades out. So maybe you're assuming it's going to fade out after you walk away, and it hasn't been. Or maybe it's bright daylight when you park the car, and you don't notice that the dome light is still on. Or maybe it comes back on by itself. And if your dome light is on for two or three days, that certainly would kill your battery.

I suppose you also can test it yourself. Sleep in the car some night, Cheryl, and bring a book. If at any point during the night you can actually read the book, you've diagnosed the problem.

Most likely, whatever is happening is happening intermittently, which is why the battery doesn't always die when you park the car for a few days. In the interim, you can buy yourself a "trickle charger," (sometimes called a "battery tender"). That's an inexpensive device you can hook up to the battery when you park the car that will keep the battery fully charged.

But for a real solution, your dealer is going to have to do a better job of tracking down the source of the power drain. And it sounds like you're going to have to insist that he try harder. If the dealer can't figure out what's draining your battery, ask the service manager who else you can speak to higher up at Ford.

If you were leaving the car for a couple of weeks and the battery went dead, I'd say that's not abnormal nowadays, given all the electronics that draw power when the car is off. But it's ridiculous for a car to fail to start after only a few days.

So let them know, nicely, that it's unacceptable to not be able to rely on a brand-new car to start when you need it. Good luck.

Get the Car Talk Newsletter

Got a question about your car?

Ask Someone Who Owns One