Two things, Audi provides a vent hose that connects to the battery (and
the Champion replacement I have) which takes the gasses out of the passenger
Second, There is no need to remove the rear seat to jump the car. Audi has
thoughtfully provided a terminal for such things. It is located in front
of the air box on the frame rail. Naturally, this is the positive terminal
since ground points are all around.
(* not really a flame, but Audi thought of these things and you did not *)