A car battery is a rechargeable cell in the SLI (starting-lighting-ignition) variety of batteries. They are also in the lead acid family of batteries.
The high power output of a car battery is necessary to supply a high current draw needed for the engine starter. A normal car battery provides about 12.6 volts and is divided into 6 separate cells; each cell produces about 2.1 volts per cell.
As the battery state of charge decreases the voltage produced also decreases.