Here are the Steps to Jump Start the Battery
The first thing to do is to locate the jump start connection points. Some models don't have it, so locate and connect it directly to the battery instead. There are four possible battery locations in a Benz: in the trunk, the engine bay, under the front passenger seat, or under the rear passenger seat.
Three Ways to Jump Start the Battery
Using jumper cables and another car. This is the quickest way to start your vehicle. However, you might run the risk of damaging your battery, shorten its life, cause electrical component malfunctions, or trigger the control units to show under voltage fault codes. If you need to get back quickly on the road, though, just make sure you use jumper cables that have low gauge rating or are made of thick wires.
Things to Remember when using this method: when connecting the jumper cables to the other car (helper car), make sure not to allow the clamps to touch together.
Never lean over the battery while you connect the clamps especially if your Mercedes model doesn't have the jump start connection points. Also, see to it that the red clamp doesn't touch the black clamp or your car's frame.
Once your car has already started, disconnect first the negative part of your jumper cables.
Read more here: http://www.niguelauto.com/info-articles/how-to-jump-start-your-mercedes-benz/