Audi A5 Alarm Failure Linked to Auxiliary Battery

As a hobby mechanic with some experience working on Audis, I dealt with a similar electrical issue on my 2017 Audi A4. The car alarm system showed identical symptoms, and the battery signal was consistently weak. After running diagnostics, it turned out the auxiliary car battery was completely drained and beyond recovery. These batteries typically last 4-5 years, so age-related failure is common. The workshop confirmed this was affecting both the alarm system and other auxiliary functions. The fix required a complete battery replacement along with a system reset. Total cost was 330 Euro, including programming and testing the new battery to ensure proper alarm system function. To better assist with your case, could you share: Current battery age, Whether you notice other electrical issues, If the main battery has been replaced recently, Whether the car sits unused for long periods These details would help determine if your situation matches what I experienced and if youre likely facing a similar battery replacement scenario.

Last service was at 107000 km, just about 1500 km ago. Thanks for the detailed information. My situation seems identical, the battery alarm warning started appearing suddenly. The auxiliary battery is original, and the car has been parked for extended periods during lockdowns which likely contributed to the battery drain. The only other electrical issue I notice is occasional flickering of the interior lights. The main battery was replaced last year, but the auxiliary one is still original from 2019. Since the symptoms match and the battery age is similar, I will prepare for a battery replacement. Understanding the typical cost helps set expectations for the workshop visit. Would replacing both batteries at once be recommended to prevent future electrical issues, or is replacing just the auxiliary battery sufficient?

Thanks for those details. With my A4, I decided to only replace the auxiliary battery since my main battery was fairly new, just like in your case. Since youve already replaced the main battery last year, focusing on just the auxiliary battery should resolve your alarm system issues. The flickering interior lights you mentioned were also present in my case, its a typical symptom when the auxiliary battery problem affects the overall electrical system. After the auxiliary battery replacement, these secondary electrical issues completely disappeared. Based on my experience, there was no benefit in replacing both batteries when one was still good. The car alarm and all auxiliary systems have been working flawlessly since fixing just the problematic battery. Its been about 18 months since the repair, and I havent experienced any battery problems or electrical issues since. A tip from my repair experience: make sure the workshop performs a full system reset and battery registration after installation. This ensures all electrical components, especially the alarm system, properly recognize the new auxiliary battery. Given the matching symptoms and similar vehicle age, youre likely looking at the same straightforward fix I had. The 330 Euro cost I mentioned earlier included this complete procedure.

Thank you all for the input. After reviewing the responses and considering my car's symptoms, I will proceed with the auxiliary battery replacement. The matching issues, particularly the battery alarm warnings and flickering lights, make it clear this is the likely culprit. Since my main battery is still relatively new from last years replacement, I will focus only on the auxiliary battery for now. The cost estimate of around 330 Euro helps set realistic expectations for the workshop visit. I will make sure to request both the battery registration and system reset as part of the service. Good to know this should resolve both the car alarm system issues and the interior light flickering. This has been really helpful in understanding what to expect and confirming that my auxiliary battery problems match a common pattern. I will schedule the repair soon and update once its resolved in case others face similar issues with their alarm system.