My daughter purchased a new Corsa 1.2 in January 2008. The car is used every day to commute to work, a round trip of 10 miles and in addition, it is used for social driving at weekends. It's normally driven in daylight hours. During the winter months she goes to work in the dark and all the electrics are used. During this period, after starting up, the alternator light continues to flash some 10 or 12 times approximately. If the vehicle is driven at weekends in the daylight with no electrics on, then for four days or so the light does not flash.

During the life of the vehicle both the battery and alternator have been changed at different times, the garage stating that both were defective. Both the current battery and alternator have been checked and are working correctly. The vehicle is parked outside at the rear of her property in the open. What is happening?