How to Check for Overcharging of a Car Battery

Save yourself future headaches by diagnosing whether your car battery is overcharging.

Car batteries don't last forever. Most quality batteries, however, should serve their purpose for four to six years. If you have a car battery that is suddenly losing its charge, is dying completely, or needs to be replaced, you may have a problem with overcharging. The overcharging of car batteries is one of the leading causes of early battery failure. This is due to a malfunctioning voltage regulator, a built-in component of most modern alternators. If overcharging is a problem for your vehicle, there is a simple, inexpensive way to check your battery.

Things You'll Need

• Voltage meter with digital readout

Instructions

1. Begin testing with the vehicle turned off. Open the hood and remove any shields that cover the battery and/or the battery terminals.

2. Place the positive lead of your voltage meter on the positive battery terminal. The positive terminal often has a red cable and is marked by a plus (+) sign. Then connect the negative lead of the voltage meter to the negative terminal of the battery. The negative terminal often has a black cable and is indicated by a minus (-) sign.

3. Look at the reading on your voltage meter. If you are using a meter with a digital readout, you should see that the battery is producing around 12.4 to 12.9 volts. This is your baseline reading. Anything less, and your battery is not fully not charged or is otherwise damaged.

4. Start your vehicle.

5. Connect the positive and negative leads of your voltage meter to the corresponding posts on the battery once again.

6. Note the reading on your meter. If the meter's readout is hovering at 14.8 volts or above, then your battery is overcharging and is at risk of being ruined. You should take your vehicle to a qualified mechanic, as the alternator may need to be replaced or, if possible, the voltage regulator.

Tips & Warnings

• Voltage meters with digital readouts are inexpensive and can be purchased at most auto supply dealers.

• If the terminals and posts on your battery are corroded (coated with a green crust), you should clean them before testing. Use a post-and-terminal cleaning tool to brush the terminals and posts. If you don't have such a tool, a wire brush or steel wool will work; just be careful not to touch both terminals at the same time while cleaning.

References

• Auto Battery Chargers: 5 Steps to Check if Your Car is Overcharging the Battery
• Car Battery Shop: Car Battery Information

Resources

• Battery Stuff: Battery Basics - How to Provide Care and Maintenance for Your Battery