Once you’re certain that you have a dead battery, the first thing you need to do is pull the running car up next to the dead car, and lift the hoods on both. Note that some manufactures (Mercedes and BMW included) place the battery in the trunk rather than the engine bay. Before you begin, make sure that both cars are off, and all accessories (lights, radio, A/C, windshield wipers) are turned off.

Attach one of the red (positive) ends of the jumper cables to the positive terminal of the good battery.

Attach the other red (positive) end of the jumper cables to the positive terminal of the dead battery.

Attach one of the black (negative) ends of the jumper cables to the negative terminal of the good battery.

Attach the other black (negative) end of the cable to a ground point on the dead car. This can be the engine block, a bolt on the car, or any exposed metal on the car.

Start the engine of the good car, and let it run for a few minutes before attempting to start the engine of the dead car.

NOTE-When attempting to start the dead car, have someone in the good car rev the engine. Revving the engine causes the car to generate more electricity, giving the dead car an easier time starting. Once the dead car is started, disconnect the cables in reverse order. Allow the jumped car to run for a few minutes before shutting it off once more. This gives the battery time to recharge.