Audi TT Aux Battery Issues Causing Multiple Failures

Having dealt with similar electrical problems on my 2013 Audi A5, your symptoms sound very familiar. I have some experience with car electronics and battery issues. The auxiliary battery malfunction symptoms match exactly what I encountered. My issues included dashboard errors, sluggish starts, and unusual electrical glitches. After initial confusion about the main battery being fine, my workshop diagnosed it as a failing auxiliary battery. The battery replacement cost me 290 Euro, including diagnostics and labor. The fix resolved all electrical problems immediately, and the car has been running perfectly since the repair. Before suggesting specific solutions, could you share: Current mileage, Service history of batteries, Specific error messages showing up, Whether problems occur more in cold weather, If you notice issues with the start-stop system A failing auxiliary battery often causes these cascading electrical issues in modern vehicles with complex electronics. Low voltage from a deteriorating auxiliary battery can trigger multiple system warnings and performance issues. This sounds like a straightforward battery malfunction, but knowing these details would help confirm if your situation matches what I experienced.

Last service was done at 39500 KM and mileage now shows 40706 KM. The electrical system diagnosis you described matches my experience exactly. After checking the low voltage readings, replacing the auxiliary battery makes sense as the next step. Have already noticed the engine start is getting worse by the day, especially during the last week. Will schedule the battery replacement based on this feedback.

Thanks for providing those details. The rapid deterioration of engine start performance you mentioned is a classic sign of auxiliary battery failure that I experienced too. With only about 1200km since your last service, this timeline matches the sudden onset I noticed with my A5 when the auxiliary battery started failing. The progressive worsening of starting performance you described over the last week is particularly telling. In my case, this rapid decline was the final confirmation before I got the battery replacement. A failing auxiliary battery often shows this pattern, working marginally for a while, then quickly degrading to cause low voltage issues across multiple systems. After my battery replacement, the engine start returned to normal instantly, and all electrical glitches disappeared. The repair cost was worth every cent considering how it resolved all the cascading electrical problems. Would you mind updating the forum after your battery replacement? It would be helpful to confirm if your experience mirrors the complete resolution of symptoms I saw with my A5. Based on the matching symptoms and similar vehicle electronics, I expect youll see the same positive results.

Based on your helpful input and my observations, I can now move forward with more certainty. The mileage difference since my last service is minimal, and the power management issues are following the exact pattern you described. The rapid decline in engine start performance this past week really concerns me, but its good to know this matches the typical auxiliary battery failure pattern. The low voltage symptoms affecting multiple systems make complete sense now, especially how they get worse each day. Since our situations are so similar, I feel confident scheduling the battery replacement as the next step. The cost seems reasonable considering it should resolve all these electrical problems at once. Will definitely post an update after the repair is done. Looking at how the auxiliary power issues are progressing, I better get this sorted soon before facing a complete failure. Thanks for sharing your experience, it helped validate what I was suspecting about the battery being the root cause.