The standard car battery has 12 volts. A fully-charged battery is essential to starting the car and provides power to the light and other car accessories.
A voltmeter is needed to test the charge of a car battery. Before testing, the car and the lights must be turned off. The owner then connects the voltmeter’s positive, red lead to the battery’s positive terminal, and the negative, black lead to the battery’s negative terminal. The voltmeter then produces a reading anywhere from 12.66 to 11.89, depending on the outside temperature. A voltage reading less than 12.45 indicates that the car battery is less than 75 percent charged and needs to be recharged. Leaving a battery at less than a 75 percent charge for more than a few days can cause permanent damage.