Your car's power station is the 12 V battery installed inside. All the electric power required for the functioning of every one of the car components is supplied by the battery. Electricity can be a terrible damsel when scorned and hence it's essential that one knows the proper procedure of handling any electrical device or appliance. An electrical battery is no exception and it needs to be handled with care.
About Car Batteries
Your car battery is a set of electrochemical cells connected together in series. Most of them are lead-acid batteries, with every cell consisting of lead and lead oxide plates, dipped in diluted sulfuric acid. Chemical reactions that occur between the lead, lead oxide plates and the sulfuric acid, make the discharging and charging of the battery possible.
Through two power terminals, one negative (black) and positive (red), the power stored in the battery is distributed to all the electrical accessories involved in the functioning of the car. The black terminal is actually the 'ground' terminal, that completes the circuit and is connected with the car chassis. Due to the highly corrosive nature of sulfuric acid and the car chassis connection with the battery, you need to take certain precautions when disconnecting the battery, which will be elucidated in the following lines.
How to Safely Disconnect a Car Battery?
There are many occasions when you may need to disconnect the car battery. One of the most common ones is the replacement of a car part like the oxygen sensor or replacement of the throttle sensor. Before I walk you through the procedure for disconnecting the battery, let me talk about the things you'll need to be equipped with. Safety goggles, a pair of rubber gloves and cleaning equipment including a brush, baking soda and soap are essential items that you'll need, besides the main tool, which is the appropriate size wrench.
Switch off the car, let it cool for some time and then locate the car battery, under the hood. Wear your goggles and gloves. Observe the black (negative) and red (positive) terminal attached to the battery, fixed with a nut and bolt arrangement.
Now that you are done cleaning the terminals, use the wrench to remove the negative terminal first. This is because the negative terminal is connected with the chassis. If you remove the red terminal first and simultaneous wrench contact with car chassis and positive terminal happens, a short circuit may result. So it's essential that you remove the negative terminal first. Just loosen the nuts enough to remove the terminal from the point of contact with the battery. Make sure that it doesn't come in contact with any metal car part.
Then you can proceed with disconnecting the positive terminal, in the same manner. Again makes sure that the red terminal too, doesn't come in contact with any metal car part, or the negative terminal! Then you may continue with your car repair job. Look for corrosive material that might have been deposited over the battery terminals and clean it up using a brush, soap and baking soda solution.
Grease the terminals with petroleum jelly to prevent further corrosion. Once you are done, make sure that you connect the positive terminal first, followed by the negative terminal using the wrench. With that, your mission is accomplished.
The key point to remember in the above discussed procedure for disconnecting car battery, is to always remove the negative terminal before the positive terminal. As discussed before, this will disconnect the chassis from the negative terminal, thereby making it safe for you to go ahead with car repair. With the proper precautions taken, you can safely disconnect the car battery without any problems. In case you are still left with any doubts and don't feel confident enough to go ahead with it, leave the job for a professional to handle. As always, it's better to be safe than sorry!