The radio in your Nissan Maxima will not work after you replace the battery because the radio has a built-in anti-theft system. When power is removed from the radio -- which happens when you disconnect the battery -- the radio is locked out and you must have the security code to validate that you are the owner of the radio before it will work again.
Locate the code for your radio. This code is given to you by the dealer when you purchase the vehicle. Usually, you can find the code on a card stored in the owner's manual. If you cannot locate the code, take a ride to a Nissan dealership. They can provide the code to you.
Start your Maxima and then turn on the radio. The radio prompts you for the code as soon as it powers on.
Enter the code using the station-select buttons on the radio.
