Battery (All): Terminology: Short-circuit
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 short-circuit is when the current takes a short cut where the resistance is less and therefore does not go via the intended route. A short-circuit can be caused for example by particles detaching from the plates in the cells. Eventually these deposits can be so large that a conductive connection is made between the two plates so that the current can flow between the two plates instead. A short-circuit in a cell can fully discharge a battery and render the battery useless.