How to Test Your Car's Battery
If you want to know whether your car's battery is in good condition or not, you can always test it with a voltmeter from an automotive store.
Before you test your battery, make sure that your car's engine and all of its lights are shut off, and you're wearing rubber gloves and goggles to protect you from any mishaps. Connect the positive and negative leads on the voltmeter to the appropriate terminals on your battery. Most of the time, the red lead will be positive, and the black lead will be negative.