Do you by any chance have the Sat Nav system? If so, I heve heard that there have been issues with it leaking a lot more current than it is supposed to and completely draining the battery in a couple of days......
If you do have that, then it is worth investigating.. Also, you may just have a dud battery..... If you don't have SatNav, then insist they supply a new battery..... This will be cheap for them and will show up if there is really a problem..
Also, do you do mainly very short journeys? If so, that can also be the problem. You must go on some long runs to ensure the battery gets fully charged..
I only use my car at weekends and I take it for a motorway run each weekend...
I never have trouble starting it even when unused all week...
I have the 2.0T..