Audi RS4 Alarm Failure Linked to Auxiliary Battery Issues

I experienced a similar battery problem with my Audi RS3 (2015). The auxiliary battery failure caused the alarm system to malfunction and eventually stop working completely. After a proper system diagnosis, it turned out the auxiliary battery was indeed the root cause, having degraded significantly over time. The repair was straightforward but required specialized equipment to properly reset the alarm system after battery replacement. This is a known issue with VAG vehicles as the auxiliary battery handles the alarm system independently from the main battery. During the battery check, the technician found that voltage output had dropped below the required threshold. The auxiliary battery replacement resolved all symptoms, alarm system functionality was restored, and no more error codes appeared. This is not considered a serious repair but requires attention since a failing auxiliary battery can eventually drain the main battery and cause broader electrical issues. The repair involves the battery replacement itself plus programming, as the new battery needs to be properly integrated with the vehicle's electrical system. Worth noting that doing a proper electrical system diagnosis first is important, as similar symptoms could occasionally stem from other components like voltage regulators or control modules.

Thanks for sharing your experience. I had nearly identical symptoms on my RS4 last month. After reading your post, I wanted to check if you remember how much the whole repair ended up costing? My mechanic quoted me 350 Euro for parts and labor, including the battery check and reprogramming. Also curious if your car has been running fine since the battery alarm issue was fixed or if other electrical problems showed up later?

The total repair bill came to 330 Euro, which covered the whole job including the new auxiliary battery, programming, and fixing the alarm system defect. This price was actually a bit better than what your mechanic quoted. Since getting the battery replaced and having the alarm system properly reset, my RS3 has been running perfectly with zero electrical issues. The battery check showed it was definitely just an aging battery problem, and once that was sorted, all the warning lights and error codes disappeared completely. I can confirm after six months that no additional electrical problems have surfaced. The car alarm works flawlessly now, and the battery holds its charge like it should. It was worth every cent to get it properly diagnosed and fixed rather than trying cheaper alternatives that might not have solved the root cause. The fact that your quote is similar to what I paid suggests your mechanic is in the right ballpark for this type of repair.

Thanks for the helpful advice. Just got back from the mechanic and wanted to share how it went. The service took about 2 hours total. They ran a full diagnostic test which confirmed the auxiliary battery was failing. Cost came to 340 Euro including the new battery, programming work, and labor. The mechanic showed me the old battery and explained how its degraded condition was affecting the alarm system. They used proper diagnostic equipment to reset everything after the replacement. Car is running great now, all error codes are gone and the alarm system works perfectly again. The whole experience was much better than my previous repair situations. No unnecessary extra work was suggested and the price matched what others paid for the same fix. Really glad I checked here first to know what to expect.