Design And Function: Principle
WARNING: This page is about a different car, the 2004 Volvo S40, 2003 Volvo S40, 2002 Volvo S40, 2001 Volvo S40, and 2000 Volvo S40. However, it is still accessible from the selected car via links, so may be relevant.
A battery is a unit which stores chemical energy which can then be converted into electrical energy as required. When the battery is connected to an external source of consumption (the car starter motor for example), the stored chemical energy is converted into electrical energy and current flows through the circuit.
The start battery in a car, the lead accumulator, is rechargeable. Such a battery can be recharged repeatedly, whereby electrical energy is converted to chemical energy.