It may well be that the battery was at fault.
Many years ago, batteries used to die slowly – this was evident from the slow cranking of the engine when starting the car, giving plenty of warning of the battery’s demise. However recently I’ve experienced a battery dying within a day; and others have told me the same – one minute the battery is fine, the next it will not even light the vehicle dash.
However before splashing out on a new battery, you should have checked the battery charging voltage on the vehicle. With the engine revs at 1,500 or more – the battery voltage should be around 14V – certainly well over 12V. If you find that the charging voltage is around 14V and after the vehicle has been left overnight, it will not start – then almost certainly the battery is being drained by something left on (such as an interior light), which will need investigation (not a new battery).