I have the same issue but mine goes flat in a couple of days...
After doing lots of research on this and other forums the most common fault's are down to the following...
1, Old alarm's and the wiring of them...
2, Old Stereo head units...
3, Other dodgey wiring...
I have put on a new batterey and checked the alternator and it cahrges at 14.5V which is correct..
I am having the alarm ripped out next week and a new one fitted, the guy who is doing it is gonna check for other drains whils he fits it and then we should find out what it is... You can check the drain by using a voltmeter on the Ohms setting's and pull fuses to see if you can source the drain...
Read this thread from the S2 forum...
http://www.s2forum.com/forum/showthread.php?t=42491I will report back after I have had the alarm changed...
HTH