Audi Q4 Battery Failures Plague Multiple Systems

I had very similar issues with my 2021 Audi Q4 Sportback e-tron last winter and can share my experience, having worked on several electric vehicles. The symptoms matched exactly, inconsistent voltage readings, unusual system warnings, and dim lights pointed to either battery health issues or a charging system problem. After monitoring the voltage drop patterns, my workshop ran a comprehensive diagnostic on the 12V auxiliary battery system, not the main high-voltage battery. The root cause was a heavily discharged auxiliary battery that could no longer maintain proper voltage levels. The workshop performed a full testing sequence of the charging system to rule out any alternator issues before replacing the auxiliary battery. Total repair cost was 290 Euro including diagnostics. Quick questions to help diagnose your case: Are the issues more frequent when starting the vehicle after sitting idle? Have you noticed any correlation between extreme temperatures and system warnings? When was the last time your auxiliary battery was tested? Which specific warning messages are you seeing? These details would help determine if your case matches the auxiliary battery failure pattern I experienced or if there might be other power supply components involved.

My vehicle has 20619KM and the last service was just completed 2 weeks ago. After reading your detailed response, I can confirm similar warning patterns, especially after the car sits idle overnight. The voltage regulator readings fluctuate between 11.2V and 12.8V, which matches the symptoms you described. The warning messages typically show Battery Management System Error and Low Voltage warnings. The auxiliary battery was tested during the last service but perhaps needs a more thorough examination since the issues persist. The technicians did mention potential voltage drop issues but focused mainly on software updates. Would you recommend getting a second opinion specifically focused on the auxiliary battery and power supply components?

Based on those voltage readings and the warning patterns youre describing, it definitely mirrors my experience. After my auxiliary battery replacement, Ive been monitoring the voltage regulator readings closely, and a healthy system should maintain around 13.2V-14.4V while running. Your readings dropping to 11.2V strongly indicates a charging system problem or deteriorating battery health. The fact that your issues persist after service suggests they might have missed the underlying cause. In my case, the initial software updates didnt resolve the voltage drop issue because the root problem was hardware-related. The auxiliary battery was actually failing to maintain proper charge despite passing basic tests. Id strongly recommend getting a specialized diagnostic that includes: Full charging system analysis, Load testing of the auxiliary battery, Voltage drop testing across all major connections, Testing of the DC-DC converter that charges the 12V system When my alternator issue was finally diagnosed correctly, the readings showed similar inconsistent patterns to yours. Given the low mileage on your vehicle, its likely covered under warranty, so pursuing a thorough charging system diagnosis would be worthwhile.

Thanks for the great technical feedback. I'll schedule a specialized diagnostic focusing on the auxiliary battery and charging system components. The voltage readings you shared as normal (13.2V-14.4V) really help benchmark where my system should be versus where it is now (11.2V-12.8V). The electrical problem seems more complex than just a software issue, and the battery voltage inconsistency matches the exact pattern you experienced. I'll have them specifically test the charging system, battery health, and DC-DC converter while documenting all the voltage drop readings. Since it's still under warranty, getting a complete diagnosis of the power supply system makes sense before any electrical issues get worse. I'll update once I have the results from the thorough battery terminal and charging system inspection.