Steinz

Hello! I have a battery drain issue on my 2005 Audi A3 Sportback. The problem started after my mechanic welded on the car. A few days later the battery was completely dead — even the LED on the USB charger was not lighting up. Here is what I have discovered and measured so far: After locking the car, there is a 4–5A current draw, the car does not go to sleep. The (factory original) RNS-E display turns off, but I can still hear the internal fan running, and the speakers are making a hissing noise. After a few minutes, the speakers turn off with a small popping sound, but immediately turn back on and continue hissing. If I pull fuse F18 (15A) in the engine bay, the RNS-E is powered down, the speakers stop hissing, and the locked car’s current draw drops to 0.7–1.8A. However, the car still does not fully go to sleep — in VCDS I can see that something wakes it up every 4–5 seconds, and I can also hear the small internal fan of the climate control module spinning up. If I disconnect the battery terminal for a few seconds and reconnect it (while F18 for the RNS-E is still removed), the problem disappears: the car goes to sleep properly and the current draw drops to below 0.00A. Other things I noticed, not sure if they are related: I get bulb-out warnings for the rear lights (license plate lights, reverse light, parking light, indicator, etc.), but it keeps changing — sometimes license plate light, sometimes reverse light, sometimes indicator. The bulbs are fine and actually work. This bulb warning already existed before the battery drain issue. Occasionally, a window switch does not work for a moment, or if it does, the one-touch auto close function sometimes does not work. Does anyone have any ideas or suggestions what could be causing this?