A school-run car does the hardest kind of driving for a battery. It starts, crawls a kilometre or two with the AC on full, idles in a queue and is switched off again. The alternator never gets a long run to put back what the starter took. After two or three summers of this the battery rests near 12.2V instead of 12.6V, and one hot afternoon it cannot turn the engine.
That is why battery testing comes before any sale. The technician measures resting voltage, cranking strength and the alternator's charging output at your car. If the battery is only empty and still healthy, we tell you so and a jump start is all you need that day.