Hi if anyone is thinking of upgrading there stereo from the early shape B6 Stereo (rcd300) to the latest shape stereo (rcd310 rcd500 etc) You will definatly need to also upgrade your "Can Bus Gateway" to avoid battery drain.
I found out the hard way when i upgraded mine and after leaving the car for 36 hours the battery was dead I bought a new Can Bus Gateway from Ebay for around £100 Was fitted and reprogrammed and works a treat so far. No flat battery of yet.