Unlock my car radio After battery replacement

The unlock code is provided with the instructions that came with the car - probably on a card along with the owner's manual. So check the glove compartment. If that fails - call the service department of a local dealer and ask how to get the code - it may require providing either the car's VIN or the radio's serial number This assumes it's an OEM radio and not after-market.

Call the dealership that originally sold the car. Radio locks are not freely shared without a lot of proof of ownership.