hey,
i had the battery drain issue on a 2006 GTi, after upgrading the RNS510 firmware to version 2600
there are two options availalbe to you.
1. downgrade the unit to version 1200, this will wipe the unit, so make sure you have the map dvd - your dealer might be kind enough to do this for you.
2. upgrade your CAN to a L or higher version CAN
check here for specific details
http://www.my-gti.com/1101 there is another option, and that is to just upgrade the unit and do nothing.
when i initially upgraded my RNS510 to version 2600, i miss read the battery drain issue.
the car started every morning, it wasnt until it sat for two days that it failed to start. not an ideal solution i know, and i am sure it is not good for the life of you battery, but it is an option too.
best of luck with it, its a 30 min job, but completely transforms the car.
there is a VCDS coding you can so as well, its something to do with speaker set-up in your car, i can not recall where i got it, but it may have been on that site above.
its worth doing, it made the sound from the unit much richer.