Audi S5 Battery Drain Mystery: Fix Hidden Issues Now

I experienced something very similar with my 2010 Audi S4 last year. Having some experience with car electronics, I first thought it was just a dead battery issue, but it turned out to be more complex. The symptoms matched yours exactly, multiple warning lights, electrical glitches, and the car battery needed frequent charging. After dealing with this for about two weeks, I took it to a workshop where they diagnosed a faulty battery sensor. This component monitors the vehicle battery status and charging system, and when it fails, it can cause all sorts of electrical issues. The repair cost me 315 Euro including the new sensor, programming, and labor. Since the fix, all electrical problems disappeared and the battery holds its charge perfectly. Before suggesting this might be your exact issue, it would help to know: Have you checked the battery terminals for corrosion? What is the age of your current battery? Are there any specific error codes showing up? Does the problem occur more frequently when cold or hot? A proper diagnosis is crucial with electrical issues, as a low battery condition can be a symptom rather than the root cause.

Last service was done at 90983 KM. Thanks for the response. The battery terminals look clean with no visible corrosion. The car battery is about 5 years old now and the problems started showing up more frequently during cold mornings. Getting error codes for parking sensors, headlight range control, and stability control system. I noticed the battery charging seems slower than usual and loses charge quickly even after a full charge. Going to have it tested, but wanted to rule out the battery sensor you mentioned since the symptoms match perfectly. Will get both checked at the shop.

Thanks for those details. That 5-year-old battery age is significant. While my S4 issue did turn out to be the battery sensor, the age of your battery strongly suggests it might be your primary problem. A discharged battery at that age often indicates its reaching end of life. When my sensor issue occurred, the battery itself was only 2 years old and tested fine. The key difference I noticed was that even a fully charged battery would drain quickly due to the faulty sensor misreading the charge state. The electrical system symptoms you describe, slow charging and quick discharge, align more with a failing battery than a sensor problem. Cold weather typically exposes battery weakness, as starting requires more power in low temperatures. My suggestion would be: 1. Get the battery tested first, most shops do this free 2. If the battery tests weak, replace it before investigating other issues 3. If a new battery doesnt resolve everything, then look at the sensor A new quality battery should cost around 200-300 Euro. Just ensure you get one with the correct specifications for the S5. The multiple error messages are typical when the electrical system voltage drops below normal operating levels, regardless of whether its caused by a dead battery or sensor issues.

Since you provided the full history of the previous messages, I'm creating the final response as (who started the conversation): Really appreciate the detailed feedback. Just got back from the shop and you were spot on, they tested both the battery and sensor. The vehicle battery was definitely at end of life, showing significant capacity loss. Battery charging was taking longer because it could barely hold a charge anymore. They confirmed the sensor was working correctly by running diagnostics. Went ahead with a new battery installation and the transformation is remarkable. No more error messages, lights are steady, and it starts instantly even in cold weather. Total cost was 285 Euro for a high-quality replacement battery with a 4-year warranty. Kind of kicking myself for not addressing the battery failure sooner, but at least its sorted now. Thanks for helping me understand the likely root cause. Having the service team check both components definitely gave me peace of mind that we tackled the right issue.