If you have an e-38, there is no radio code. There is a starter disable code. This code has nothing to do with the battery. It is there for you to set for the period of time that you park your car. You pick the code each time, -right before you exit the car. You then must re-enter the code in order to start the car when you come back. Once this is done that code is meaningless. You decide the code each time you use the feature. You can use a different one each time. Go ahead and disconnect your battery. Just make sure the doors are unlocked. :)