How to Check a Car Battery

If your car is having trouble starting or won't start at all, one of the first things to check is the battery. To do this, you don't have to remove the battery from your car, though it is recommended. However, the steps are the same whether you remove the battery or not.

Things You'll Need

• Volt meter
• Battery charger
• Half-inch open-end box wrench

Instructions

How to Check a Car Battery

1. 

   To remove a battery from your car, start by undoing the positive and negative terminals. The battery is held in place with battery bracket bolts. To undo these bolts and remove the car battery, standard terminals require a half-inch open-end box wrench.

2. 

   Once the car battery is removed, use a volt meter to check how many volts the battery has. At this point, your car does not need to be on.

   Hold the volt meter to the car battery's positive and negative terminals, using the volt meter's color-coded prongs; red goes to the battery's positive terminal and black goes to the negative terminal. The volt meter's display will tell you how many volts your battery has. It should read about 11 to 13 volts.

3. 

   If your car battery reads less than 11 volts on the volt meter, it needs to be charged completely on a battery charger. Just like the volt meter, a battery charger has a red cable and a black cable. Attach the red cable to your car battery's positive terminal and the black cable to the negative terminal.
   Battery chargers have different charge settings to choose from. Choose a setting between 20 and 40 amps; this will charge the battery in a couple of hours. The battery charger will indicate when your car battery is completely charged.

4. Once your car battery is fully charged, use the volt meter to recheck the voltage by conducting what's called a load test. Hold the prongs of the volt meter to the corresponding battery terminals and watch the volt meter while someone else starts your car. Make a note of how low the battery voltage drops. A normal car battery will drop to 10 or 11 volts. If your battery voltage drops below 10, this is a sign that it needs to be replaced.

5. If your car battery has passed the load test---meaning it did not drop below 10 volts during the test---reinstall the battery. If your car battery has failed the load test, you will need to purchase a new car battery and install it.

Tips & Warnings

• Your local auto parts store offers a free service to check, charge and load-test your car battery. In some cars, the battery is not located in a convenient spot. Check your owner's manual to locate your battery and for removal instructions.

• Battery acid is dangerous and can burn your skin. Wear rubber gloves to avoid exposure. In older vehicles, battery cables could be corroded and it can be hard to see whether the battery cables are red or black; in this case, look for the plus or minus sign. When using the box wrench, be careful not to connect the battery terminals; this could cause a spark.