Installing a winch, so figured I'd test my battery and alternator. Battery is reading 12.6v when the truck is off, which I think is perfect When the engine is running (at idle) I'm reading 13.99v - I thought a healthy alternator should be between 14.2 and 14.5v? Does the mean the alternator is starting to go? This is on a gen1 (2004). I know some cars have variable output alternators, does the 1st gen Xterra?