The first proper frost every year, the phone does not stop. Same call, over and over. Turned the key, got a click and a groan, nothing. And nearly every one of them is a battery that was already tired in October and nobody checked it.
That is the thing about winter car problems. They are things that were quietly going wrong for months, and the cold just finished them off. At around freezing a battery loses roughly 40 per cent of its capacity, while the engine needs more power to turn over because the oil is thicker. Less power available, more power needed. Add a heater, lights and a demister all running at once and the weak link shows itself, usually on the coldest morning and always when you are late.
So the check is not clever. It is the same list a good mechanic runs through in the autumn anyway, done properly, with a load tester on the battery and a refractometer in the coolant rather than a glance and a guess. If the car had a full service in the last few months, say so when you ring and we will probably tell you to keep your money and have the free battery test instead.
Everything on this page is cheap in October and expensive in January. That is the whole argument.