The battery is considered dead when there isn't enough charge to start the engine or run electrical components.
Normally, the first sign is dim lighting in the interior of the vehicle, and when you try to start it, the engine may crank slowly, or not at all. A very rapid clicking noise is normally heard if there is any charge left in the battery, but in many cases the vehicle will be completely unresponsive.
If the
battery is losing charge while driving the vehicle, the battery warning light will illuminate, and the engine may stall.