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How to Replace a Battery

By Joe Ballard
Published on July 8th, 2024

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There are numerous straightforward repairs that you, as a capable car owner, can confidently tackle on your vehicle. Changing a battery is one of the most straightforward. The ability to handle these repairs yourself empowers you to save significant time and money by not taking your car to the shop for minor issues. The range of repairs you can handle will depend on your automotive DIY skills, the vehicle's year, make, model, and a suitable working area.

Car battery replacement

In this article, we will guide you through the warning signs of a failing battery and how to replace it, further enhancing your control over your car's maintenance.

How do you know if the battery is bad?

I have stated in previous articles that a lead-acid battery will usually provide warning signs that it is going bad. Some of these symptoms of potential failure include the following:

  • The engine turns over slowly
  • Dim or flashing headlights
  • The Check Engine Light or battery warning light comes on
  • The battery is more than three years old
  • One or more of your car's accessories are malfunctioning (radio is at the top of the list)

It's crucial to be proactive and watch for these warning signs. As a DIYer, you have the tools and knowledge to diagnose battery issues before they become major problems. For instance, using my Mazda Miata as an example, I connected my Innova 5610 scanner and RepairSolutions2 app on my iPhone to run the Battery/Alternator Monitor test. Using the Innova 5610 OBD scanner, the Battery test results indicated that the battery was BAD. This result was surprising as I had no problems starting the car.

To ensure that the charging system (alternator) was working correctly, I performed the Alternator monitor test, and the results indicated that the charging system was GOOD. This reliable diagnostic process reassured me that the battery may be weak and should be replaced soon. By following these steps, you can also feel confident in the accuracy of the diagnostic process and secure in your decision to replace the battery.

Innova 5610 paired with RepairSolutions2

Find the perfect scanner in 1 minute

How do you replace the battery?

In my Mazda Miata, the battery is located in the trunk. It is located there because there is no room for it in the engine compartment, so I guess it makes sense. Whether the battery is located in the engine compartment or the trunk, the same rules apply when replacing it. Remember, sulphuric acid is explosive, so take care not to generate any sparks during the replacement process. Let's take a look at the steps involved:

  • Safety First: If possible, park the vehicle on level ground and wear safety glasses and gloves to protect your eyes and hands.
  • Locate the Battery: Open the car hood or trunk (Mazda Miata) and locate the battery. It is usually pretty easy to find and accessible, as it needs to be replaced periodically.
  • Disconnect the Negative Terminal (-): This is a crucial step to avoid any short circuits and sparks that could create a safety issue. Disconnect the cables from the battery using the proper wrench, starting with the negative terminal. It is sometimes recommended that you tie off the negative terminal cable so that it does not accidentally come into contact with the negative terminal post (black) during removal.
  • Disconnect the Positive Terminal (+): Using the same wrench, disconnect the positive cable from the positive terminal (red).
  • Remove the Battery: A bracket holds the battery in place, and the design will vary depending on the manufacturer. Remove this bracket, clamp a vice grip onto one of the terminal posts, and lift the battery out of the battery compartment. The battery may be pretty heavy depending on the vehicle, so use caution when removing it.
  • Prepare the New Battery: To ensure the new battery is correct, simply place them side-by-side to ensure the size is the same and the terminals are correctly situated on the battery. If you consulted a guide at the parts store before buying it, it should be the correct battery for your vehicle.
  • Install the New Battery: Assuming the battery is physically correct, clamp the vice grips on a battery terminal post, place the battery in the tray, secure it with the original clamp, and remove the vice grips.
  • Connect the Cables: Always connect the positive cable (red) first. Sometimes, the terminal connector at the end of the cables may have some corrosion. If there is corrosion, clean that off before connecting to the battery terminal, as this will ensure a good tight connection. Now, connect the negative (black) cable to the negative terminal. Putting a dab of grease on each terminal post after you connect the cable to the terminal post is a good idea to prevent corrosion.
  • Car Battery Coding: You may need to code the new battery for some vehicles. This can be done using an OBD2 scanner to tell the vehicle's ECM that a new battery has been installed. You will also need to reset your clock and any other electronic devices that were temporarily disconnected from power during the battery replacement.

Key Takeaways

Replacing a battery is a very straightforward process and can easily be handled by a DIYer. The typical cost to have a shop replace a battery is approximately $290-$300 (labor $40-$55 and battery $250). The DIY cost is the battery cost only $250, so the DIY savings is about $50 (labor). There is no specific replacement interval for batteries. However, some factors can affect their longevity, including how often you start your vehicle, the climate in your area, and how you maintain the starting and charging system.


If you notice any potential failure warning signs associated with your battery, you must take action as soon as possible. If you observe any warning signs of an imminent failure, you will usually have some time to react and prepare for the replacement. If you ignore the warning signs, you may, at best, get stranded, or worse, you could experience a complete failure of all your vehicle's electronics. Using your OBD scanner to periodically check your battery status or get it checked by an experienced service technician is always a good idea.

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