Read the Owner's Manual Before Heading to the Auto Parts Store

Dear Car Talk: After six and a half years of driving my 2015 Audi A4, I decided to replace the battery. I got a replacement battery at my local auto parts store and swapped out the batteries.

When I looked in my owner's manual, I was surprised to learn that the new battery needed to be "registered" in the car's computer system, otherwise -- the manual said -- the car's battery management system wouldn't work properly.

I took the car to a local mechanic who specializes in German cars, and he told me that in order to register the battery he needed an 11-digit part number, a three-digit vendor number, and 10 digit serial number. The battery I bought at the auto parts store had none of these numbers on it, and, according to the company that made it, those numbers are not available for their batteries. I then called the Audi dealer, who told me they could register the battery for $240. I only paid $200 for the battery!

What's the story? Do I need to register this battery in the car, and what happens if I don't? -- John

Audi's got you over an Ingolstadt beer barrel here, John.

The reason they want you to enter the battery's details is so the charging system knows that you have a new battery and knows the battery's specifications.

Why does that matter? Well, an older battery on its last legs needs to be charged more intensively, to keep it working. And if the Audi thinks you're still using your old, 6-year-old battery, Audi says it could overcharge your new battery, and possibly even damage your $600 alternator.

We're told that some aftermarket batteries will provide the information the Audi computer needs, in which case any shop (like your German car specialist) that has Audi's diagnostic software can do the update for you.

But since you did what most screw-it-up-yourselfers do (screw it up first, read the instructions later), you bought a battery before figuring out what you actually needed. What can you do now? Well, you can genuflect to the Audi dealer. You can buy another aftermarket battery that provides the information you need. Or you can take your chances and drive it, and hope you sell the car to your no-good cousin Buford before it becomes a problem.

If you're really stubborn, and feel lucky, I suppose you could take the numbers off of your old battery, perhaps changing the last few digits of the serial number, enter those numbers, and see if your Audi "accepts" that as a new battery with the same specs.

That would be sneaky, and I have no idea if your computer would accept it, or if it would protect the new battery correctly. So I can't recommend you try that. But I understand how it might be tempting to try it instead of spending $240 to have the dealer do something similar -- a workaround.

Next time, ask your German car specialist to steer you toward an aftermarket battery that has the necessary documentation. It sounds like he's read the manual. Good luck.

Ready for a new ride? When the time comes to part with your old car, donate it to your favorite NPR station. They will turn it into more of the programs you love. Here's how.

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