[jmatta]

My friend did the same thing several years ago on his '02. If you reinstall the battery, you will be fine; no need to position the ignition key. Yes, the cumulative data in the ECU will be gone and will take at least a week of various driving conditions to rebuild. IN my friend's case, the car would not pass emissions since the ECU status did not contain enough driving history to clear ready codes. As far as the immobilizer, that is all contained within flash memory, so it will not be an issue.