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How to Connect Car Batteries: A Comprehensive Guide

How to Connect Car Batteries: A Comprehensive Guide

There are a lot of how-tos and do-it-yourself tutorials available online today. From how to repair certain small car parts to how to replace major car components. Instead of paying someone to do it, you can opt to do it yourself. It can be pretty useful since labor costs are not that cheap. However, when it comes to connecting car batteries, it is not done like other maintenance and repair tasks that have instructions with no specific order. The process on how to connect car batteries safely can be a bit of a challenge since any wrong move can cause your electric system to be burned and other serious issues. It is important that when you connect your car battery, you need to make sure that you will connect the positive terminal first then the negative terminal.

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How to Connect Car Batteries: The Safety Measures


There are a lot of reasons why car owners disconnect the batteries from their vehicles. It might be because they have to charge the battery, check it, or to replace it. Whatever the reason why it was disconnected, you should know how to connect car batteries properly and safely. The process can be pretty easy but you need to do it the right way by following the instructions in the right order. 


But before we proceed to learn how to connect car batteries and know its procedures, there are some things that you need to do first. You need to prepare the area and do some precautionary measures to make sure that you and your car will be safe. 


Although the process of how to connect car batteries is pretty easy, you still want to do it properly since the amount of current the battery is capable of is quite massive. You don’t want to do anything that can damage your vehicle because of short circuits and other issues. It is recommended that you always check your owner’s manual for any specific safety precautions.  


To start, you have to make sure that the area that you are working on is properly ventilated and is on a level surface. If you are working in your garage and not in an open area, make sure that there is no open flame close by. Do not let any sparks of flames near the battery. Do not smoke in the area nor work on a battery with a lit cigarette in your mouth and don’t let anyone close by smoke. 


Aside from making sure that the area you are working on is safe, it is also necessary to make sure that you are protected. You should wear safety gears such as safety glasses or goggles and gloves. Wearing goggles can protect your eyes in the event of tiny errors such as accidentally mixing up the positive and negative cables. This can cause the battery to heat up and blow up that can spray its stored chemicals or water. Wearing gloves can protect you in case the battery bursts or leaks. You will also have to remove any metal jewelry off you such as bracelets or rings to ensure your safety.


You should refrain from having direct contact with any battery fluids. Keep in mind that whenever you are charging, testing, or connecting a battery, you should never lean over it. Batteries are known to be filled with sulfuric acid that produces hydrogen gas. In the event where you get acid deposits on your skin or clothes while you are working on a battery, make sure that you wash them off with water right away.  


Next thing that you need to prepare to proceed with the process of how to connect car batteries is to prepare the right tools. To make sure that you will have what you need, you can prepare tools such as socket wrench and sockets, spanner set, large crosshead screwdriver, large flathead screwdriver, wire brush, and a petroleum jelly or white lithium grease. 


When working around a car battery, you also need to be mindful of your tools. Be wary of what touches where. You need to remember that the wrench or any tool should not connect the positive and negative terminals as well as to connect the positive terminal to a metal ground on the car. You might think that all these precautionary measures are a bit too much and troublesome but doing all of these can keep you from having serious injuries and can keep your car from severe damages. 


How to Connect Car Batteries: Which Battery Terminal Do I Connect First?


Once all the safety measures are considered and done, you can proceed to connect the battery. To make sure that the process is done safely, follow these simple instructions on how to connect car batteries:

  • Turn off the car and remove the keys from the ignition.


Before you connect the battery to your car, you need to make sure that all the car’s electrical equipment such as the lights, radio, ignition system, and air conditioning are turned off. You need to remove the keys from the ignition to be sure. If you are working on a vehicle that uses FOB or Frequency Operated Button with keyless entry, make sure that the FOB is placed two meters or more away from the vehicle. 

  • Clean the battery terminal posts and cables. 

It is always a good practice to check and clean the battery terminal posts before you proceed to connect the battery. Check for any dirt, build ups, or corrosion on the battery terminals and the accompanying cables. 

If they need cleaning, you can clean the battery terminal posts and the cables by using a mixture of water and baking soda with a tool that is made specifically to clean battery terminals. You can also use a wire brush to clean it. To make the water and baking soda cleaning solution, you just need two cups of water and add one tablespoon of baking soda. This cleaning solution is known to be effective in cleaning corrosion and dirt. After cleaning the terminal posts and cables, remove the baking soda solution using a damp rag. You can also clean clamps and the battery tray.  

For added protection, you can use or apply corrosion protection products to the terminal posts and cables after cleaning. There are lots of these products sold in the market today. Whether you choose a corrosion prevention cream or spray, make sure that you apply it to the battery’s positive and negative terminals. You can also apply it on the inside of the wire connectors from the car. 

  • Examine the cables for any signs of cracks or damage. 

Aside from cleaning the terminal posts and cables, you also need to inspect the cables for any signs of cracks or damage. Examine each one closely and if you see any cracks or damage, replace the battery cables

  • Put the battery in place.

Once everything is clean and the damaged cables have been replaced, it is time to put the battery and secure it in place. To do this, find the battery tray first. You can usually find it toward the engine bay’s front and in the back of one of the headlights. There are newer vehicles with batteries that are installed in the trunk or in the cabin for a better distribution of weight. 

When you put the battery, make sure that you position it correctly by matching the terminals to the battery cables. Position it well so that the positive terminal will be on the same side as the positive cable as well as the negative terminal will be on the same side as the negative cable. Remember that the red cable is always the positive cable and black is the negative cable. 

Be careful when you carry and put the battery in place. Use both of your hands since car batteries are heavy. Make sure that you won’t drop it since it can lead to a disaster. You need to ensure that the battery tray is empty and that the cables are tucked off to the sides. Once done, secure the battery in place. Batteries usually have hold-down brackets that can go over the top. Secure it tightly, make sure that it is snug so the battery does not move around. 

  • Connect the car battery.

These instructions on how to connect car batteries need to be followed in order. It is done to ensure your safety and the safety of the vehicle. There are people who are not sure and keep asking which battery terminal to connect first. The answer is you need to connect the positive terminal to the positive post first. You can then use a wrench to tighten its connection by turning the bolt on the connector clockwise until it is snug. 

Once done, you can now connect the negative cable to the negative post. Tighten the connection as well by using a wrench after you press it to the terminal post with your hand. If for some reason the battery cable does not reach at its corresponding terminal, it could mean that the battery was not positioned properly. It has to be positioned properly.

It is important that you don’t allow anything that is made of metal to touch the terminal posts. Be careful with the tools you use. Do not let it touch the positive terminal, radiator, or any other metal surface. This can lead to a short circuit that can result in an electrical arcing and burns. In some cases, it can cause your battery to explode or destroy your car’s onboard computer. 

  • Check if the electric system is working properly.

Assuming that you already double checked the connections, ensuring that all are connected properly, you can now check if the car’s electrical system is working properly. Put the key in the ignition and start your car. Try to turn on any of the car’s electronic systems like the radio or air conditioning and make sure that they are all working. If possible, measure the output of the battery by using a multimeter.  

How to Connect Car Batteries: Why Do You Connect the Positive Terminal First?


It has been mentioned a lot of times that the procedures on how to connect car batteries must be done in a correct manner and order. If you fail to do so, it can cause harm to the car, its components, and it can even cause injury to you. But people still ask, why do you need to connect the positive terminal first? 


 There had been some debates on what battery terminal to connect first. There are people who say that it does not matter which one gets connected first since there is no circuit made yet when you only connect one wire. The statement can be true, there might be no circuit yet, but it is possible to complete the circuit. You don’t want that. You know what they say, it is better to be safe than sorry. 


The explanation why you have to connect the positive terminal first is because the negative wire is the designated ground wire. Connecting the ground wire first will cause the circuit to become completed when it is time to connect the positive wire. This can cause sparks to occur. The sparks can shock you or short out the battery as well as the other car components. To prevent this from happening, you need to make sure that you will connect the positive terminal first.  


Knowing how to connect car batteries can be very beneficial. You get to save some money by doing the task yourself instead of paying a mechanic. Knowing how to connect car batteries does not only help you every time you replace a car battery, but it can also be applied when you have to jump your battery. The process is the same, you will have to connect the positive first and then the negative. The process applies for both the good and dead batteries. However, when you disconnect a car battery, you always have to disconnect the negative first before disconnecting the positive.