08 f150 5.4 104,000 miles. Changed the serpentine belt then drove about 20 miles when the battery light came on for a couple of minutes then went off. Drove for about 10 more miles and the the radio starts turning off and on then goes off completely. Let it set in the driveway over night and the battery is dead this morning.

Could I have done something when changing the belt to damage the alternator. Checked all the connections and everything seems tight.

 

Sounds like you missed the alternator with the new belt!

 

either its a real coincidence, or you pulled a wire loose or bent it on the alternator. There are a couple different connectors. I would look closer at them.

 

I think it may have just been a coincidence. Only had 12 volts at the battery with truck running. Took it to o'reillys and had it tested. It failed so I got a new one and now I have 14 volts with the truck running. The shaft didn't seem to be bent, the pulley spun true and was tight. That's just how my luck goes.

 

on "average" alternators last about 150K miles... some go longer, some earlier.

 

Funny how things go sometimes. Easy to see how that would kind of freak you out. But when in doubt, get it tested, which is exactly what you did.