Hi, The suggestion to pull individual fuses while watching the amp meter or test light is a good one. Note, some items normally draw current, such as the clock, but not enough to drain the battery in normal use.
How long does it take for the battery to drain? Overnight or days?
For some obvious places to check: - If draining overnight, check that the dome light, glove box light, and trunk light are turning off when the door or hatch are closed. It may sound obvious, but it's happened. In our '85 Golf a youngster turned on the dome light to "all ways on" thinking it was the "door actuated" setting. The battery was dead by morning. More chronically, on our glove box, the door is warping from constant pressure on the light switch. I'm expecting the door to warp enough for the light to stay on.
- A long shot, did you replace the radio? Some new radios go into standby which draws current instead of turning completely off.
- If draining rather slowly, check the alternator, it may not be charging. Again consult Bentley for diagnostic steps.
Good luck.