Why does my Audi 80 not start after replacing the battery?

I recently replaced the battery in my Audi 80 and now it won't start. The lights and electronics work fine, but when I turn the key, nothing happens. How can I fix this issue?

Check the battery terminals for corrosion and clean them with a wire brush. Corrosion can prevent a proper connection between the battery and the car's electrical system.

Make sure the battery is installed correctly and securely. If it is loose or not connected properly, it may not provide enough power to start the car.

Check the battery voltage with a multimeter. If it is below 12.6 volts, it may not have enough charge to start the car. Recharge or replace the battery if needed.