Over the years, I have seen it time and again. An indicator that the battery has a somewhat limited life span. Sure enough, it will keep on starting your car, and you may listen intently - is everything sounding right ? Do you have your doubts regarding the state of the battery ?
I reckon I have worked it out. When you come to start your car in the morning, take a close look at the rev counter. If the rev counter needle swings up sharply towards 3-4 thousand revs, returns back to say 500...