When the engine is turned off, a fully juiced-up car battery voltage measures up to about 12.6 volts. The 12.6 volts is labeled as a “resting voltage”. When the car is turned in, the voltage usually rises up to 13.5 or 14.5. This usually happens due to the alternator of the car. There are 6 cells that are present inside of a battery and each of these cells holds a 2.1- volt. So all of them placed together comprise a 12.6 -volt automotive battery. Each of those six cells is made up of at least one positive plate and one negative plate. Inside these cells are insulating separators that prevent the positive and negative plates from touching. All of these sex cells are submerged in an electrolyte fluid that is a mixture of sulfuric acid and water.