Design and function: Principle
WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. 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.