Batteries can crap out on you with little to no warning. Age doesn't mean squat these days. I've had batteries that lasted 2-yrs and some that lasted 10. It's the pick of the draw.,,,and luck, of course.
I've found at times, the battery could indicate a full 12.5-13 volts, but as Steve suggested, it could have a bad cell.
I've found at times, the battery could indicate a full 12.5-13 volts, but as Steve suggested, it could have a bad cell.