How to Diagnose Car Battery Trouble

Having trouble with your car battery? Don't stress it too much. Usually, a malfunctioning battery is fairly easy to diagnose, even for those with limited mechanical ability. If the problem exists only with the battery, the solution ranges from recharging to replacement. Ultimately, you can check the battery using a few simple tools that can be purchased any automotive supply store. Also, if necessary, you can replace the battery on your own, thus saving yourself an expensive trip to the mechanic.

Things You'll Need

• Voltmeter
• Battery charger
• Post and terminal cleaning tool or small wire brush
• Distilled water (for standard-duty batteries only)

Instructions

Basic Battery Diagnostics

1. Turn off all of your vehicle's accessories, including radio and lights, and attempt to start the engine. If the engine sounds strong, but simply fails to fire, your battery is fine. Be careful, however, not to continue trying to start the car, as it will eventually drain the battery. If the engine sounds sluggish, slowly fades or does nothing at all, then chances are your battery is dead.

2. Turn your headlights on without trying to start the vehicle. Step outside and examine the headlights. If the lights are strong, your battery is charged. If, however, the lights are dim or not working, the trouble lies with your battery.

3. Open the hood on your vehicle and remove any shields from the battery. Then examine the battery. Specifically, look at the battery's terminals. Corroded or dirty terminals are sure to cause battery trouble. Use a post and terminal cleaning tool or small wire brush to clean the terminals. You may need to unhook the battery cables in order to do this properly. Also, make sure the battery cables are securely fastened to the posts.

4. Check the fluid level in the battery (for standard-duty batteries only). If you own a maintenance-free battery, simply skip this step. Pry the caps off the top of the battery and look into the cells. You should see plates within the battery, as well as fluid. Add distilled water to the cell if necessary. Add only enough distilled water to cover the plates (See Ref. 1). Use only distilled water, as tap water will promote corrosion.

Using a Voltmeter to Diagnose Battery Troubles

1. Remove all guards that are covering your battery and double check to ensure your ignition switch and all accessories are turned off.

2. Check your voltmeter to ensure it's set to 12 volts (some voltmeters have multiple settings) and connect the positive probe to the battery's positive terminal. Then connect the negative probe to the negative terminal. Make sure the probes have a good connection to the battery.

3. Read the display on your voltmeter. A working battery with a full charge should display a reading of 12.5 to 12.8 volts (See Ref. 2).

4. Recharge your battery if you see a reading of 12.45 or lower. A reading of 12.45 indicates that your battery has only a 75-percent charge. If you see a reading of 12.24, your battery is less than 50-percent charged (See Ref. 3). Thus, your charging times will vary according to how badly your battery drained. If your battery drains again, without having been used in your vehicle, then it needs a replacement.

Tips & Warnings

• Car batteries generally last 4 to 6 years. If you have a battery in this age-range, or older, your troubles are likely associated with age. In this case, simply install a new battery in your vehicle.

References

• Check that Car: Checking Your Battery
• 2 Car Pros: How Do I Check My Car Battery?
• AA1 Car: Diagnosing a Car Battery that Runs Down