Unlock your vehicle and go to the driver's seat. Locate for the hood release and trunk release of the vehicle. Then pull the release lever of the hood and the trunk.
Battery In the Trunk
Open the trunk and pull up the floor mat of the trunk. Once you pulled up the mat you will find the battery beside the spare tire of the Mercedes-Benz SL-Class R230.
The main battery is used to start and keep the engine running.
Engine Bay Battery
The second battery can be located in the engine compartment. Pull the hood release under the dashboard and go in front of the vehicle. Unlock the hood latch and pull up the hood. Then find the battery on the passenger side of the engine compartment.
The battery in the engine bay is also known as the auxiliary or secondary battery. It is used to power up the electronics.