2003 6.0L powerstroke single alternator. So was driving yesterday, and the battery light came on when foot was out of the throttle, put my foot back into it and the light went off.

I got home and plugged in my scan tool and monitored the voltage, I never got low volts, just was at 12.6 at idle with all the power on, seat heaters, fan full blast etc. While driving it was getting 14 volts.
Tonight I plugged in the scan tool after sitting for 8 hours. So on cold start the first 5 seconds of engine on it got 11.6 volts. I sat there and it went right up to 12.6. So should I replace my alternator?

 

sounds like its about to take a crap. id check your connections first though just to be safe.

 

Check batteries first, if one is shorted internally it will draw a lot ! Charge over night then load test in am, then still check alternator even if you do replace a battery or both. I personally replace both unless they are pretty close to new. Bad batteries can kill your alternator as they draw a heavier load than normal. I can recommend DC Power if you need an alternator as they are made better from new, not hopped up stock parts. Just my .02$ ..

 

Drove it today only was at 13.5 volts, both batteries are new, truck is all stock. So I imagine it's just the alt going bad. Thanks for the input guys!