Battery (All): Terminology: Short-Circuit
WARNING: This page is about a different car, the 2010 Volvo V70, 2009 Volvo V70, and 2008 Volvo V70. 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.