As Petso referred to above, you need to back feed power into the electrical system of the car. What you need to do this can vary from car to car. You can find the 9 volt lighter plugin adapters at Amazon and other places but they do not always work. You may have to turn on the ignition switch to pull all the electrical relays on so that the voltage can get to all the memory locations in the car. It is not just the radio but the engine, transmission, power windows locations, and the heater controls that can have memory set for them.How do you change the battery and not lose all settings radio channels?