The common story is simple. A family parks at dusk, an interior light or the parking lights stay on, and five hours later the car only clicks. Most of the time a jump start is all it needs. The technician boosts the car and checks the alternator before you join the queue for the exit.
If the battery is at the end of its life, the boost will not hold and the car may stall in traffic leaving the car park. In that case the technician can fit a new battery there in the bay. Have the car's make, model and year ready when you message, so the right size is on the van.