I have a F150 2000 5.4L that is having charging system problems. We are constantly getting the battery drained. The alternator was just replaced 3 days ago, the cables all check out. The strange symptom is that when we increase the rpm of engine, the alternator gauge goes to "H" position then battery light comes on and everything blinks. The battery charge lvl when idling is around 15.2 volts. The voltage at starter is also 15.2 so no losses throught the links. Anybody have any more ideas?

BTW we took the battery in last week before doing the alternator and it tested good.

 

Have your battery load tested. Sounds like you have a shorted cell in it.

 

Sounds like you also got a bad replacement alternator (defective regulator). A good one would never exceed 15 volts on charging regardless of the battery's condition. Keep running it as is and you'll fry your electronics.

Also, check fuse F11 in the underhood box. If open, the output voltage can go up.

Steve