Several days ago we had a mysterious dead battery on our A6 4.2. No accessories had been left on, and the battery (with a rated life of 85 months) was only about 35 months old. There was no obvious explanation. I jumped it and drove the car at highway speeds for several hours, and all seemed fine (restarts were no problem). However, the following morning the battery was dead again.

Then it occurred to me that the night before the battery croaked, I'd had the car hooked to VAG COM for about 10 minutes to pull all the stored codes from the car. I ran the process with the engine off and the A/C system off but with the key in the "run" position.

Is it possible that the process of going through all the modules weakened the battery substantially or pushed an already comromised battery over the edge?

When the repair shop put the old battery on their tester, the report was that it was marginal. For what it's worth, the technician who replaced the battery checked the car's amperage draw on the new battery while the car was off (and after all the onboard computers had gone to sleep, which took about 15 minutes), and he said it was reading about 75 miliamps. Is this normal?

TIA