Audi Q5 Aux Battery Issues Causing Power Problems

Had a very similar issue with my Audi Q7 2019 diesel. With some experience working on car electronics, I initially thought it was just the main battery, but the symptoms you describe match exactly what I encountered. The power management system was showing various faults, and the auxiliary battery malfunction caused multiple electrical issues. My workshop ran a complete diagnostic on both batteries and found the auxiliary battery was completely depleted, affecting the entire electrical system. The fix involved: Full diagnostic scan, Replacement of the auxiliary battery, Recalibration of the power management system, Testing of the charging circuit Total repair cost was 290 Euro, which included parts and labor. The issues were completely resolved after the replacement. Before giving more specific advice, could you share: Current mileage on your Q5, Specific error messages you are seeing, Whether the issues occur more frequently after short trips or longer drives, If you have had any recent electrical upgrades installed These details would help determine if your situation matches what I experienced with my Q7 and whether additional components might need checking beyond the auxiliary battery.

Thanks for your reply and sharing your experience. My Q5 just hit 159658 KM after the latest service. The voltage drop and power management issues definitely match what you described. The error messages appear more frequently during cold starts, especially after the car sits idle overnight. The engine start performance has become noticeably weaker over the past few weeks. I checked the workshop manual and it suggests auxiliary battery replacement around 150000 KM, so the timing aligns with the symptoms. Your repair cost of 290 Euro seems reasonable considering the diagnostic work and recalibration needed. The battery failure signs started showing up gradually without any electrical upgrades or modifications. Looks like I should schedule a proper diagnosis at a workshop soon before the problems get worse.

Thanks for providing those additional details. Your situation sounds nearly identical to what I experienced, especially with the cold start issues and gradual onset of problems. My Q7 also showed the first signs of battery failure during cold mornings, and the power management system began throwing more frequent errors as the auxiliary battery degraded. The workshop confirmed this is a common wear pattern around the 150000-160000 KM mark. After my repair, the voltage drop issues completely disappeared, and the electrical system returned to normal operation. Just ensure the workshop performs the full power management recalibration after the battery replacement, this was crucial in my case for resolving all electrical gremlins. A quick tip from my experience: Consider having them check the main battery health while they are doing the work. In my case, while the auxiliary battery was the primary issue, the main battery was also showing early signs of wear. Getting both checked can prevent future starting problems. Based on your mileage and symptoms, this definitely sounds like the same auxiliary battery issue I faced. The 290 Euro repair cost should be fairly consistent since its a standard service procedure.

Thank you for the detailed feedback about your Q7 experience. After reviewing all symptoms and comparing them to my Q5 situation, I feel more confident about the diagnosis. The shared pattern of voltage drop issues and electrical system behavior is particularly telling. My auxiliary battery is definitely due for replacement based on the 150000 KM service interval recommendation. The cold start problems and battery failure indicators match the typical wear pattern you described. The gradual progression of electrical gremlins also aligns perfectly with your experience. I will schedule the workshop visit this week and make sure they perform: Complete diagnostic scan, Auxiliary battery replacement, Power management system recalibration, Main battery health check The 290 Euro cost estimate gives me a good baseline for the expected repair budget. It helps knowing that the fix resolved all electrical issues in your case. Definitely worth addressing now before the low voltage problems worsen and potentially affect other car electronics. Thanks again for sharing your insight. Will proceed with the repair following your recommendations.