Dear Car Talk:
The battery in one of my vehicles is nearing the end of its life. What is the best way to preserve the electronic presets (radio, lights settings, etc.) when the battery is disconnected during replacement? -- Tim
Take it to a shop that has the same little device we have, Tim. We have a small power pack that plugs into the car's data port, and when the ignition is off, it trickles a small amount of power to the car's computer.
That way, while the battery is removed, you keep your radio presets, your clock and any other memorized customized seating, door-lock or lighting preferences that your car allows you to set these days. Your computer also will retain the car's performance parameters.
Lots of cars these days "learn" your driving style and set things like transmission-shift points based on that. The computer also stores sensor and emissions data that you'll need when you get your car inspected.
Granted, it doesn't take more than a day or two to re-acquire that information, but it's one more benefit of maintaining minimal power during a battery change.
Most shops will have one of these devices. And if you want to, you even can buy one yourself. I've seen a "home" version for about $20 that runs on a 9-volt battery and plugs into the car's cigarette lighter. Then you can be known throughout the neighborhood as the guy who saves radio presets.
I will warn you that it works about 95 percent of the time. For some reason, it fails occasionally, and then we have to set all of the customer's presets to NPR and convince him that that's all he's ever listened to. So we hope it works for you, Tim.