RS7 Starting Issues: Battery Terminal Power Drop Fix

Had a similar issue with my 2014 RS6 last winter. Having some experience with electrical issues, I initially thought it was just the starter motor, but it turned out more complex. The symptoms matched exactly, slow cranking, clicking sounds, and irregular power supply readings. After checking the fuse box and all visible connections myself, I took it to the workshop since the ignition switch was also acting up intermittently. The diagnostic process revealed a heavily discharged battery that was beyond recovery. The constant drain had also put extra stress on the circuit breaker system. The workshop did a full electrical diagnostic sweep and found: 1. Main battery was failing to hold charge 2. Power supply system showing inconsistent voltage 3. All other components (starter motor, alternator) were actually fine Total repair cost was 290 Euro including diagnostics and new battery installation. Before suggesting specific fixes for your RS7, could you share: How old is the current battery? Any recent electrical upgrades or accessories installed? Does the problem occur more after short trips or long parking periods? Are you getting any warning lights on the dash? This would help narrow down if you are facing the same root cause or if there might be other factors involved.

Thanks for the detailed response. Latest service was at 123000 KM, about 3 months ago. Actually found the root cause, it was indeed a charging system issue, but not the battery itself. The power supply was being interrupted by a corroded ground connection at the transmission mount. The short circuit was occurring intermittently due to moisture exposure. After cleaning and properly securing the ground point with dielectric grease, the starter motor is engaging perfectly every time. The voltage readings at terminal 30 are now stable at 12.6V. Total fix cost was 120 Euro for diagnostic and repair. Sharing this in case others run into similar symptoms.

Good to hear you tracked down the root cause! Had the exact same issue on my RS7 last year, that ground connection is a known weak point. The electrical fault symptoms were identical, right down to the unstable terminal 30 readings. The wiring harness routing in that area makes it particularly vulnerable to moisture buildup. Smart move using dielectric grease, I ended up having to replace the entire ground strap on mine since the corrosion had worked its way into the cable. That repair ran closer to 200 Euro. For anyone else seeing these symptoms, checking ground connections should be step one before assuming battery or starter issues. A short circuit from a bad ground can mimic a lot of other electrical problems. The transmission mount area is especially prone to corrosion due to heat cycling and environmental exposure. Those stable 12.6V readings are exactly what you want to see. Regular checks of the charging system voltage can catch these issues early before they cause starting problems.

I really appreciate all the feedback, particularly about the ground connection issues. Your responses helped confirm what I discovered. Just to close the loop on this, absolutely right about checking ground connections first. The transmission mount ground point was completely corroded, causing a short circuit that mimicked more serious electrical problems. After fixing the ground and applying dielectric grease, the wiring harness and all electrical systems are working perfectly. The voltage drop at terminal 30 has completely stabilized at 12.6V, and the starter motor engages instantly every time. Total repair was very reasonable at 120 Euro compared to what it could have been if I had started replacing major components. Definitely saving that tip about regular charging system voltage checks. Much easier to catch these issues early than deal with no-start situations. The fuse box and other connection points all tested fine, it really was just that one ground point causing all the trouble.