GMC Repair: dead battery- boosted - wont read electronic key, emergency road service, dash lights

Question
We were attending a wedding, and by mistake did not turn the ignition off all the way, after rolling up the windows.  Only after 5 hours did someone announce on the mike, that a Cadillac had it's lights on in the parking lot.  Emergency road service was called through On Star, and all my dash lights came on with the boost, but message centre said something about it couldn't read or find my electronic key...so it still wouldn't start.  Also a message about anti-theft deterrent came on.  Of course we were 50 km's from home, so now had to wait for a taxi too... When battery goes dead, does it automatically require a full re-diagnostic or should we try to boost it ourselves today.  I have a 2008 CTS.

Answer
you may have to relearn the key to the car, try leaving a booster on the car and the key in the ignition for ten minutes in the forward position, where all the dash lights come on, if it does not start after that you may have to have it towed to a dealer for a relearn