kind of funny as your description did not sound particularily like a bad battery. Quote: you were driving around and the radio went out etc. As long as you were driving the alternaor should have been putting out enough in combination even with a marginal battery to keep the radio functional. Although a need to get a battery jump to start a day earlier could easily have indicated a bad battery. Always best to get a battery charged and checked prior to changing it if not sure as that service is offered free at a lot of places.