Hmmm...so my issue is that EVERYTHING lights up. The headlights come on, nothing dims, radio plays, sunroof opens/closes. It doesn't act like the battery is dead. HOWEVER - it is a 2013 and it did occur to me that it needed changing. I was being lazy and waiting for warmer weather to change it since it looks like a pain in the ass.Dead battery. I accidentally discharged my battery last year, overnight, from a Friday to Saturday. Everything you described was the same for me. But I realized it was my fault, I left the door ajar, I was using VAGCOM in the garage, and I intended to come back, forgot, and the interior light, and parking lights (which were on) drained the battery.
After two hours on a charger, it started right up. I hope it's just that for you. Batteries can only be expected to last about 5 years. Sometimes less in severe duty (really cold or really hot) conditions. I am going to replace mine next Fall before the winter strikes. Fortunately for me, I have a 100 amp load tester, and a hydrometer, and optical refractometer. This is because I own a travel trailer and have to care for two 6 volt golf cart batteries. My charged Touareg battery measured fine after a full charge (later that weekend I put it on the charger overnight to make sure it was 100%).
As far as the other post - no other backstory. Wife drove it, parked it as usual in the garage. Went out the next day to start and everything lights up it just doesn't turn over. No other work has been done recently. It does have an aftermarket remote start which it has had for 1.5 years and a hardwired radar detector which has been on it it for 2.5+ years.