The biggest challenge you might encounter when attempting to charge the car battery in your Audi is actually finding the battery. Audi manufacturers cover the engines with bonnets that need to be removed to gain access into the engine compartment after you've opened the bonnet. In some of the 8-cylinder Audi's, you may go through all that only to find out the battery is in the boot on the passenger side. Refer to the owner's manual for the location of the battery in your Audi before getting started.
Locate the battery in your Audi and expose it by removing anything in the way, such as the engine bonnet of cover.
Adjust the settings on the battery charger to accommodate the battery in the Audi. Each charger has different options, but you want to make sure it's on 12-volt, conventional (not deep cycle) battery and choose an amp setting. The higher the amp setting, the quicker the charge. The lower the amp setting, the longer the charge. Choosing around 10 amps to charge it for a little while would be good unless you're trying to start it sooner.
Place the red clamp of the charger onto the positive terminal end of the battery. This will have a red lead cable and the "+" insignia stamped on the battery housing.
Place the black clamp of the charger onto the negative terminal end of the battery. This will have a black lead cable and the "-" insignia stamped on the battery housing.
Be sure the wires from the charger on the cables are not in the way of any moving parts when the Audi is started.
Plug the charger into an electrical socket or extension cord. Many chargers are active once you plug them in. Some chargers have a timer you need to set in order to turn them on and still others might have a power button. Allow the proper time to charge the battery. It will depend on how dead the battery is and what amp setting you chose. Charging 10 amps on a completely dead battery would take an hour or two.
Start the Audi after the battery is charged. Unplug the charger from the outlet or extension cord. Remove the black clamp from the negative terminal. Remove the red clamp from the positive terminal. Replace the cover over the battery and close the bonnet or boot.