Most car batteries function because they contain lead compounds and acid for creating power. The battery powers the lights and the devices in the car when the engine is off and then it re-charges from the alternator when the car is running. There are thick cables, which connect the battery to the alternator and the electrical system of the car. The terminals of these cables are connected with the positive and negative terminals of the battery.
In order to disconnect the terminals of top mounted batteries you need to place the car in an aired are to locate the battery. Then you have to use a box-end wrench in order to loosen the clamp on the negative terminal of the battery. Continue by lifting this terminal up. Sometimes it will not come easy, so move it back and forth for a little while. Make sure the negative cable is safely put aside and it does not touch the negative battery terminal. Repeat the same procedure for the positive terminal.
Removing the terminals of side mounted car batteries is almost similar. Make sure that the car is in such an area where air blows. Disconnect the cables with a wrench and pay attention so that do not accidentally get in contact with the terminals on the battery. Start with the negative cable and then repeat the operation for the positive one.
It is very important to take all safety and precautionary measures when working with car batteries. The ground cable is the one that should be removed at the beginning. For the great majority of the cars, this is the negative cable, but there are also models with a positive ground system. If you are unsure which system is on your car, check the manual or ask your dealer.
If there is corrosion on the battery terminals, you can clean it using a baking soda solution.
Be careful because the gas resulting from lead-acid batteries is toxic and can explode. Always keep the car in an air area and always wear safety equipment. If you have to work in the garage, you should open all windows and doors.