Guys the battery in your key is simply to operate the infrared remote control to unlock and lock the car and activate the alarm - THAT'S IT. It has no effect on the starting of the car. If the battery in the FOB is dead or completely removed from the key the car will still start. The integrated chip in the key makes contact when its inserted into the ignition switch with the cars computer through the use of the cars own battery not the battery in the key.

The Smartkey used in all MB's that's an electronic key is the one that if the battery in the key dies then the car won't start.