How to Test a Car Battery the Correct Way

A battery like any other car part is going to wear out over time. In different regions of the country and the world, the battery will wear out faster. In Florida, for example it is hot virtually all year round. The heat from the engine, the ambient heat from the air, and the reflective heat from the road will kill a batteries life in a very short time. If you get a year out of a battery, you are doing pretty well. Since the light on your dashboard does not have a meter, and the volt gauge only reads the alternator, how can you tell if the battery is good or if it is going bad? You have to know how to test a car battery so grab your multimeter and follow along. If you do not have a multimeter, you can pick up a cheap one from any hardware, auto part, and most department stores.

How to Test a Car Battery

Safety First

I have been a mechanic for the better part of two decades. I have seen too many people think they know how to test a car battery when they really do not and get hurt doing it. Being educated is being safe and that alone is a top priority. Here is a list of items you should have before you do anything with a battery.

  • Safety glasses

  • Terminal cleaner for top post or wire brush for side post

  • Wrench (the correct size)

  • Multimeter

  • Hand towels or rags

  • Socket set with 4″ extension

The Steps

  1. Locate the battery’s negative battery cable. Regardless of if it is a top post or side post the cable should be black. If there were modifications done and you have two red or two black, the battery will always show a (-) on the negative side.
  2. Remove the negative terminal. At this point you can grab your terminal cleaner or wire brush and clean off the dirt or corrosion from the battery. Corrosion is what is formed when there is a bad or loose connection or resistance of any kind.
  3. A good rule to follow is to wrap the negative terminal in a rag. The negative terminal is the ground. Since there are plenty of items on the engine, frame and supports that are used as a ground, if the negative touches them it will cause a connection and you want to avoid this.
  4. Remove the positive battery cable and clean it off and also clean the battery post off.
  5. Grab your multimeter and set it to the 50 volt scale. Refer to the owner’s manual to determine which one that is.
  6. Take the black lead and the red lead and place it on the respective positive and negative terminals.
  7. Wait 15 seconds and look at the meter reading. The battery should be at least 9.6 volts. Any lower and this indicates the battery needs to be replaced, or will need to be replaced shortly.
  8. If the battery is good, do these steps in reverse order. The negative should always come off first and go on last.

Testing a car battery is quite an easy task with the proper tools. There are some people that do not feel comfortable doing it themselves (which is perfectly fine). If you don’t feel comfortable doing this yourself then many auto stores will do it for you; depending on where you go there could be a fee involved. Be sure to take your time when doing the process. Since the battery terminals are damaged, replace them before reconnecting the battery. A loose connection will hurt the battery and could cause injury if the wrench slips from a rounded off bolt. The terminals are usually about $5 a piece and are easy to change out. Just remember, knowing how to test a car battery can mean a car starting every time or being stranded in a dark parking lot with a dead battery.

Category: Tutorials

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