Audi Q8's Battery Alarm Failure After 150K km

Had a similar issue with my 2019 Audi Q7 3.0 TFSI. The electrical issue started with intermittent alarm system failures before the complete shutdown. The auxiliary battery was the root cause, not the main car battery. The problem required a full diagnostic scan which revealed multiple stored errors related to the voltage supply system. The auxiliary battery specifically powers the alarm system and other security features when the main engine is off. Its failure creates a cascade of electrical problems. In my case, the repair involved replacing both the auxiliary battery and its control module, as the original unit had degraded beyond acceptable parameters. This was not a quick fix, the entire system needed recoding after component replacement to ensure proper communication between modules. The issue is relatively common in these vehicles once they pass 130000km. While serious enough to require immediate attention to prevent security system failure, its not a structural or engine-related concern. The repair process is straightforward for technicians familiar with Audi electrical systems. Most importantly, the auxiliary battery replacement must be properly coded to the vehicle system. This prevents future electrical issues and ensures all security features function correctly.

Thanks for sharing your Q7 experience. Dealing with a very similar situation now on my Q8. After reading your detailed explanation, I am pretty sure the auxiliary battery is also my culprit. The car alarm issues and system diagnosis showing power supply errors match exactly what you described. Did you manage to get it fixed for good, or have you experienced any recurring issues since the repair? Would be helpful to know the repair cost too, so I can budget accordingly for both the auxiliary battery and potential control module replacement.

Following up on your cost question, I got my Q8 fixed last week and can confirm the repair solved both the battery alarm system problem and the auxiliary battery issues completely. The car alarm is now working perfectly, with no recurring trouble codes in the system diagnosis. The total repair came to 330 Euro, which covered replacing the aged battery that was causing the discharge problems. The mechanic confirmed what I suspected, the auxiliary battery was definitely the source of those system warnings. The additional battery alarm defect that kept popping up has been fully resolved with the replacement. The repair shop completed the proper coding and system integration, which is crucial for these auxiliary battery replacements. Since the fix, all electrical systems and security features have been operating exactly as they should, with no battery signal issues or warning messages. If your symptoms match what I experienced, you should expect similar repair costs. Just make sure your chosen shop has experience with modern Audi electrical systems, as proper coding after the battery replacement is essential for a lasting fix.

Thanks for the input. I finally got my Q8 repaired last Monday. The electrical issue turned out to be exactly what was discussed, a failing auxiliary battery causing the battery alarm problems. Found a certified shop that specializes in Audi systems and they handled it perfectly. The complete repair, including parts and labor, cost me 375 Euro. They replaced the auxiliary battery and recalibrated all systems. The technician showed me the old battery which had significant wear, explaining why the battery signal kept failing. They also performed a full system diagnosis to ensure no other electrical issues were present. The whole repair took about 3 hours. Since then, no more battery problem warnings and the alarm system works flawlessly. Really glad I sought advice here first, helped me avoid unnecessary repairs and find the right solution quickly. The car battery warning lights have stayed off and all security features are functioning normally. Definitely recommend getting this fixed at a shop familiar with Audi electrical systems. The proper coding after replacement makes all the difference in preventing future issues.