Hey Luke!
Car batteries are a lot more durable then normal accumulators. Nonetheless car batteries are no performance parts, so they end they sometimes decide to end their life after 5-7 years. It must be something with your battery or spark plug. Spark plug only if you have a Diesel.
If it worked after charging it up then it is probably the battery. Interesting tough - my grandfather had exactly the same problem with his
A6. It's 6 years old now and one day he wanted to drive, the
A6 just wouldn't start. He recharged it once and then hasn't had any problems afterward - it never happened again. Very strange problem indeed.
A battery isn't really a performance part, and although some will disagree I would just buy a compatible unit from an autoparts store and save anywhere from 50-70% of the dealer price. 5 minutes to install and you are golden....and most auto parts stores will even do the install for free (just be sure you have your radio code handy). I am not sure, but there might even be instructions in the
A6 manual.
Hope I was able to help you a bit.
Yep, we do not have much traffic yet. But with people that return every day, we might get more in the future. Juergen and me are doing the best (Father and son that love Audis :P). Just ask if you have any other problems and visit us frequently, that would help already I guess. (Ctrl + D if you want to bookmark us hehe.). Anyways, check out:
http://www.go-audi.com/album.php - you can upload pictures of your audi over there.
Hendrik