Audi RS5 Alarm System Failure Linked to Auxiliary Battery

Having seen this exact issue on my 2014 Audi RS4, I can share some relevant experience as a weekend mechanic who does basic maintenance. The auxiliary battery problem is quite common in these models. When my car alarm started acting up, the first sign was unusual activation followed by complete system failure. The workshop first ran a complete battery signal diagnostic to isolate whether it was the main or auxiliary battery causing the issue. They confirmed the auxiliary battery had degraded beyond acceptable levels, which is typical around the 6-8 year mark. The repair involved: Full diagnostic scan, Removal of old auxiliary battery, Installation and programming of new unit, Battery check of main battery to ensure no cascade issues Total cost was 330 Euro including parts and labor. The car alarm system worked flawlessly after replacement. Before offering more specific advice, could you share: Current mileage, Whether you notice any other electrical issues, If the main battery has been replaced recently, When the problems first started occurring This information would help determine if your case matches the typical battery problem pattern these models experience.

Thanks for sharing your experience. My current mileage is 180402 KM and last full service was done 3 months ago. The battery alarm issues started about 2 weeks ago with occasional false triggers, now progressing to complete failure. No other electrical issues noticed so far. The main battery was replaced during the last service, but the auxiliary battery was not checked then. Based on your repair cost breakdown, this seems like a manageable fix. Good to know the electrical issue was isolated to just the auxiliary battery in your case.

Thanks for those details. Given the timing of your main battery replacement and the fact you had no auxiliary battery inspection during service, this really mirrors what happened with my RS4. The progressive failure pattern you describe, from unusual triggers to complete system failure, is textbook for an auxiliary battery problem in these models. The alarm system often shows these exact symptoms when the auxiliary battery voltage drops below operational levels. Since your main battery is new, we can likely rule out any cascade electrical issues. My system diagnosis experience suggests the 180000+ km mark is a common point for auxiliary battery replacement, especially if its the original unit. During my repair, the workshop confirmed that false triggers are actually a built-in failsafe when the auxiliary battery starts failing, its basically the alarm system alerting you before complete shutdown. One thing I learned: while the auxiliary battery replacement fixed my car alarm issues completely, its worth having them check the voltage regulator during repair. It only adds about 15 minutes to the diagnostic time but ensures the new battery charges properly. Based on your symptoms matching mine exactly, and considering the vehicle age and history, you can likely expect a similar repair cost around 330 Euro for the complete fix.

Thanks for the detailed information and matching experience. The timing of the electrical issues right after my main battery replacement but without an auxiliary battery check makes perfect sense now. The progression you described from unusual triggers to complete car alarm failure matches my situation perfectly. Since my car is showing the exact same battery problem symptoms at 180000+ km, I will definitely get the auxiliary battery checked and likely replaced. Good tip about having them inspect the voltage regulator during the repair, I will specifically request this when I take it in. Seeing how the issue was resolved in your case with just the auxiliary battery replacement for around 330 Euro gives me confidence this is a straightforward fix. Will schedule the repair this week before the car alarm system fails completely. Really helpful to know what to expect at the workshop and that this is a common issue with a clear solution.