If you turn the key in the ignition of your Audi A4 and the car does not start, you may have a weak or dead battery. You may need to replace the battery to fix the problem. Removing the battery to recharge or replace it is a straightforward task.
Raise and secure the vehicle's hood and locate the battery compartment, which is covered with plastic trim, located against the firewall at the back of the engine, on the passenger side.
Remove the rubber seal strip that runs across the top of the firewall with your hands.
Remove the plastic trim that covers the battery compartment and brake fluid reservoir by hand. Lift the trim up and out, toward the front of the car.
Locate the cabin pollen filter cover under the windshield, on the passenger side, next to the battery compartment. Remove the bolt from the top of the filter cover with a socket wrench, turning counterclockwise. Remove the filter cover.
Remove the three Phillips-head screws from the passenger-side windshield cover. The cover is a thin strip of plastic trim located at the bottom of the passenger side windshield. After the screws are removed, lift off the cover.
Remove the negative (black) terminal clamp from the battery with the socket wrench, turning counterclockwise. Remove the positive (red) terminal clamp with the socket wrench, turning counterclockwise. Pull the battery drain hose out of the plastic nipple on top of the battery. Use a socket wrench with an extension to unscrew the two bolts on each side of the battery that hold it to the frame. Pull the battery up and out of the compartment.
While you have the pollen filter cover off, consider replacing the filter; it may save you a job in the future.