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Check your alternator. if it failed, the truck would be running only off the battery and would eventually die, even driving down the road, if the alt quit. Should be 12.6 volts approx, with engine off. and approx 14 volts running. anything less than 13.8 volts, Id replace the alternator, but check all your connections first and if the alt. belt is slipping.
being the battery is almost 4 years old it could have lost its crack capacity. I had batteries drop a cell before and it just happens out of the blue with no warning. As the other guys are saying put a volt meter on the battery to check the alt