Replace battery for keyless remote for GM Cars?

Generally the solution to these problems is don't disconnect the battery from the car. In order to change you battery you need to connect a small 12 volt battery to the terminals before you disconnect the car battery. It need not be a large battery since the drain will be minimal and the time short. A set of flashlight batteries works fine. Mercedes are particularily difficult because you loose the radio among other things if you disconnect the battery. You must get a dealer to reset it. This negates anything you save by installing your own battery. Note a battery charger also works.