Battery keeps going dead
 

Hi there, I have a 2005 Audi A3, 2l FSI and had it for about 18 months now. I've noticed a few problems with the car, but not sure if they are linked to a reoccurring flat battery. I should say I replaced the battery about 1 year ago on advice of the audi garage.
Firstly, the dashboard back light flickers when the head lights are on. If I turn the dimmer dial to the brightest setting it doesn't flicker. I have also noticed when the battery went dead the last time, after jump starting it I drove it for 1 hour and it didn't flicker at all, since then its started flickering again. The garage says I need to replace the dimmer, though don't think this would cause the battery to go flat.
Secondly, I have noticed that the hazard light stays illuminated once the car is locked and this can be for well over an hour after the car has been locked. I have also noticed it sometimes goes off and on again of its own accord. The hazard light seems to come on when the flashing diode on the dashboard isn't flashing.
I have taken the car to both an audi garage and a private garage and both have carried out diagnostic tests and battery drain test and said there is nothing wrong with the car. Obviously there is if the battery keeps going flat. Not wanting to run up huge bills whilst the garage plays around with my car, I'm hoping someone here can help.