Well, it's not called Bimmerblog...

But I'll try to help anyway--I had a visitor yesterday who ran into this problem: my battery died in my 750il now my radio won't play.

Our intrepid querist found Revolvoblog because I had the same problem when we changed the battery in our Odyssey. As far as I can tell, most new car radios have this marvelously inconvenient feature that requires you to input a code number into the radio if it has ever been disconnected from a power source, ostensibly to keep someone from boosting it. There is supposed to be a place in your owner's manual or radio manual where this number is recorded and you can keep it in a safe place, but if you've purchased a used car this might not be available. I found our Honda's number quite by accident by catching a glimpse of a sticker on the inside of the glovebox, and figuring it wouldn't hurt to try it. If you can't find the number at all, I think about the only solution is to go to the dealer and have them figure it out, but look through your glovebox materials first.

If you anticipate unhooking the battery, a handy gadget to consider is one of these doo-lollies that feeds a small amount of 9V power back into the system through the cigarette lighter. It's kinda pricey at 16 bucks, but if you're handy it sure looks like you could make one yourself from stuff you already probably have taking up space in the spare parts box.

Anyway, there you go.