Car batteries can degrade in quality over time, so it is important for you to know how to check a car battery to make sure that it does not need maintenance or replacing. To check the battery in your car, you will need a car battery tester with a multimeter that features both a voltmeter and an amp meter. The following set of step-by-step instructions will give you all the information you need to properly check your car battery.
Look over the battery to see if there are any obvious problems you can see, such as scratches, bulges or dents. Batteries damaged in this way are not safe to use and should be replaced. Look at the metal terminals on the top of the battery to check for corrosion or oxidation. If there is a lot of corrosion, you can clean the terminals with a toothbrush and a mixture of water and baking soda.
After fully charging the battery overnight, connect the positive lead on your multimeter to the positive terminal on the battery, then the negative lead to the negative terminal. With the engine off, the surface voltage should be around 12.5 to 12.8 volts.
The alternator is the part of the engine that is connected to the drive belt and rotated when the engine is running. It uses this rotation to generate voltage, which is used to recharge the battery while the car is running. If the alternator is not working properly, the battery will drain while the vehicle is in operation. With the leads of your multimeter still connected to the battery, turn the engine on and let it idle. The voltage measurement should now be between 13.6 and 14.3 volts. To check the amperage output of the alternator, switch the multimeter to the amp meter setting and turn on all electrical accessories in the car. Check your alternator to see that this reading is consistent with its labeled maximum amperage output. If either of these measurements are off, there is a problem with your alternator.
Open the caps on the electrolyte cells in the battery to make sure there is enough electrolyte solution. If there is not enough electrolyte, you can top off each cell by adding distilled water. Use a hydrometer to make sure sulfation, or the process of sulfuric acid breaking down into other chemicals, has not occurred. The reading should be around 1.215 to 1.28, and a reading of less than 1.175 indicates that sulfation has indeed occurred and the battery needs to be replaced.
You should check your vehicle’s battery approximately every six months, and most batteries need to be replaced every three to five years. If you need to replace your battery, make sure that the new one has all the same electrical specifications and physical dimensions as the old one. Whenever you work with a car battery, remember to wear rubber gloves and proper eye protection to avoid hurting yourself with the battery acid.