before you remove the old battery, you need to keep the power on. so turn on the ignition so that you can leave the radio on. Before this go to an auto parts store and buy an adapter that will plug into the cigaret lighter (12 volt power outlet where you probably have your radar detector plugged in) attach a 9 volt regular battery to this gizzmo then take the old battery out and quickly say 5 minutes or so put the new batt in and hook it up. Most important is to reconnect the vent hose to the new battery, if there is one like on my C280. Remove the adapter and you are ready to take off. The computer will remain as it was and maybe re-program a few things, but this should not be a problem.