The battery in my wife's Zafira is playing up.

Once the car is stopped and left alone, with nothing on, there seems to be no problem, car starts fine every time. But if (as I have done twice now) put the radio on for 30 mins max whilst washing / cleaning etc, when you come to start the car again, the battery seems more or less dead. The central locking, ignition lights, indicators etc may or may light, starter motor clicks and will not turn. Jump start works every time and give it a 10-15 minute drive, battery is as good as new (providing you do not do any of the above!).

Before I go and splash out on a new battery, is this just likely to be a battery at the end of its life or something more technical / sinister?

Thanks.