I've been having an intermittent problem with the electrical system on my '16 A8 Stingray. Around a month ago I had a doctor's appointment about 35 miles from my home. When I got out of the car and attempted to lock it, I didn't hear the fuel door lock motor activate. I just assumed the key fob battery was dead but after the appointment when I attempted to open the door, the doors were locked. After accessing the door release in the rear compartment and opening the driver's side door and then placing the key fob in the pocked in the steering column I realized it wasn't a key fob battery. The entire electrical system was not working. After getting a Uber ride home I returned to the car the next day with some diagnostic equipment and after unlocking the rear compartment with the key fob key, I immediately saw the rear cargo lights were illuminated. I was able to start the car using the key fob and unlock the doors with the key fob. It seemed the electrical problem had resolved itself. Yesterday when I got in the car the dash illuminated but when I pushed the Start button I heard what sounded like a solenoid click and then the doors locked and the dash went blank. That is the fifth time this same thing has occurred but thankfully four of the times occurred while the car was in my garage. It seems to be something in the anti-theft system. I bought the car new and this problem started a little over a year ago. I was wondering if anyone else has had this problem? I'm kind of afraid to leave home in it now.

 

How old is the battery?

 

These computers on wheels will suffer all sorts of electrical glitches when the battery gets a little weak.

 

15 Months. I put a new battery in the car July 7, 2023.

 

Check the negative battery cable and positive connection point , make sure they are tight , also check the nuts on all the fuses that mount on top of the battery . I bet one is lose

 

Battery life is variable as in all things chemical and mechanical. Especially if you have an undiagnosed electrical drain in the system.

I’ve been lucky and still have my original OEM battery in my 2017 Z06. But I expect it will fail at any time now.

Your symptoms point to a weak battery. Replace it, or if you want, charge it. And see what happens.

In any case, you need to assess your charging system, and if good, figure out why the battery is discharging abnormally.

 

I agree with a full inspection of the battery and condition first!

For me, I have to tell myself how a seemingly good battery, may not be good enough for the microelectronics circuits that control our electrical systems. It's easy to check the voltage of a static battery and to see 12+ volts on a DVM and to call it good. But the health of a battery can only be confirmed by a load test. The load test tells the story.
My suggestion is to load test the battery first, and it it passes then charge it fully with a 'Battery Charger', NOT a battery tender.
Continue other electrical test on the charging system if necessary.
Afterwards, the electrical problem may be resolved.
Best of luck for a good solution.

 

All true above, and it doesn't matter how "old" ones battery is; that is the starting point with these things, as are the battery terminal connectors. That said, the positive terminal "mess" with the separate "L"-plate is a source of many problems, especially if fully disassembled when doing a battery change as most "help" sources recommend (but NOT really needed to change the battery). Making sure all the "plate" pieces actually make could connections can be trying, but necessary. If all else is good this is something else to explore. All the best (it took me several days to sort out).