Why won't my Audi A1 start after replacing the battery?

I recently replaced my Audi A1's battery, but now it won't start. I checked the connections and they seem to be secure. What could be the issue?

It's possible that the new battery is not fully charged. Try charging it for a few hours before attempting to start the car again.

Check the battery voltage using a multimeter. If it reads lower than 12 volts, the battery may need to be replaced.

Make sure the battery terminals are clean and free of any corrosion. Use a wire brush to scrub away any build-up.