battery discharges fast

[BobBobson]

As a first step I’d be doing a parasitic draw test as described here:
https://youtu.be/lRcj1fQcWwU

The problems that you’ll have are keeping the car ‘asleep’ while you carry out the test (which is why he latches all the doors etc) and also that there’s about a million fuses in a C6 chassis car!

You could also try disconnecting the battery and leaving it for a day or two just to make sure it’s not self discharging.

[ATinOf]

Common causes of battery drains for A3 A4 are radios, for Skoda's it's door looms, for TDi s its convenience module. Not heard of any specifics for 6s. As already mentioned check drain current value at rest, if you want a comparison figure I can get you one off mine at the weekend if you still have the problem.

[c3nturi0n]

Is it 'slow' to start?

If so it may be linked to an alternator that is slow charging.

[welwynnick]

Sometimes it's the alternator itself that's responsible for the discharging. Not quite so easy to test for.