Only had the car a couple of months and just ran into my 1st issue. Got back to work last night and unlocked doors with fob, put key in ignition to start and everything went dead. No lights, nothing. Checked to make sure i didnt leave lights on all day but they were off. Want to check battery but dont have a trunk key to get to it. Can you lend any advice

 

The ignition key should also fit in the trunk lock. Look right above the license plate. There should be a lock cylinder pointing almost straight down.
Also, there's most likely battery jump terminals under the hood. Not all A8 have them for some reason though. They will be either on the right or left area near the shock towers. Hook jumper cables or a battery charger to them. Look for a red plastic cap of sorts. The ground can be hooked to any bare metal surface. Then use the power trunk release.