Safety Precaution #1
Before disconnecting your car battery read the car owner’s manual first. Most commonly (if not stated otherwise in the owner’s manual) the negative cable is to be disconnected first and then the positive cable.
When you re-connect the battery, connect the positive cable first and then the negative cable.
If done in the wrong order it may affect your car’s fuses and other electronics.
Also, remove your car keys from the ignition before working on the battery. Some cars are more sensitive to this procedure than others – like German Luxury Cars (Mercedes Benz and BMW type cars) – so use extra caution.
Safety Precaution #2
If you are charging a battery do it in a well-ventilated area.
If you are handling a car battery that is installed you should open the hood of the car for a few minutes to allow for ventilation first.