Autos - How to Test for a Bad Car Battery

How to Test for a Bad Car Battery

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Test your dead battery to see if it should be replaced or restored.

dead battery image by Katrina Miller from Fotolia.com

When your car battery fails to perform, you may think about charging it. There is, however, a good chance that your battery needs to be replaced and not simply charged. Modern batteries rarely fail to work properly unless there is damage to some component inside of the battery. Charging a bad battery might allow you to start your vehicle and drive it back to your home. However, it may not prevent you from being stranded on your next trip. Testing your battery will help you determine if the battery should be charged or replaced.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Workbench
• Protective eye wear
• Battery post/terminal cleaner
• Battery load tester
• 6/12-volt battery charger/starter

1. Open the car hood. Put on safety glasses. Remove the battery cables with a wrench. Remove the battery from the vehicle and place it on your workbench.
   
   
2. Clean the battery posts. Use a battery post cleaner to clean oxidation and corrosion from the posts. Push the cleaner onto a battery post and start twisting it back and forth until the post becomes bright and shiny. Repeat the process for the other battery post. For a side mount battery, use the wire brush on the reverse end of the cleaning tool to scrub the battery's cable mounting surface. Use this brush to clean the battery cable ends of either battery type.
   
   
3. Complete a load test. Connect the positive clamp from the load tester machine to the positive battery terminal and the ground clamp to the battery's negative post. Switch the load tester to the "On" position and push the test button. If the needle drops below 12 volts and remains there, the battery must be replaced. If the needle drops and returns to 12 volts, the battery can be restored.
   
   
4. Charge the battery. Place the battery on a slow (trickle) charger. Leave the charger on for a minimum of eight hours and ideally for 24 hours to restore a dead battery. When finished, remove the charger and reinstall the battery in your vehicle.