About 2 weeks ago my battery light came on when driving than went off. All quiet for a week and it happened again. Now it is coming on every time I start vehicle...not right away sometimes and it will still go off when driving and come back on.

Had truck to 3 different places to check. 3 Different meters all showed the battery as being good (which is only about 3 months old) and alternator is charging everything fine.

Disconnected the battery the other day to replaced 4WD Solenoid so it was put back in assuring all wires were tight and posts are clean. Seems there is no rhyme or reason to it coming on. Started truck today and it idled for about 5 seconds and popped on. Comes on even when not under a full load (No AC on No Lights on) Dash gauge shows just over half and not noticing any problems with starting or anything.

Any ideas?

 

How old is your rig?
No need to start engine or have key in the ignition for preliminary checks.
Use a multimeter to check continuity of battery ground cable to ground and all ground straps (engine block, frame and body ground connections). (set ohms scale @1K or higher)
Set voltage scale @ 20 volts to check battery to alternator wire. Slip red probe into alternator boot and ground negative probe momentarily. Reading should indicate 12+volts.
Check for loose connections.
If everything checks out OK.....
Have your auto parts retailer perform a load test. This is free at most auto parts outlets.
Finally check instrument panel for a circuit short or loose hot wire that may be causing your alt. light to illuminate.

 

Sorry - it is a 2005 FX4

When I took it to Autozone they did do a test of battery and alternator under a full load and still passed.

 

Go back to Autozone and request a ODB II scan and a printout in the event any codes have been logged.

 

The Battery light comes on for a reason...either the Battery is not charging properly or it is getting ready to die.. perform the troubleshooting as DIY told you..

 

Yes they did do that scan and gave me the printout showing output on alternator and everything still looked good.

 

So the scan didn't show any codes?
I recommend you purchase a Chilton's Manual covering the 2005 F150, either from Amazon.com or Autozone, and find the current track for the battery light in the wiring diagram. It should indicate the color[s] of the wire supplying voltage to this light.
Inspect the entire length of this wire for damage and any signs of chaffing/rubbing on the instrument panel circuit board, particularly the current track for the battery light.
An intermittent or constant ground may be causing this light to illuminate, or you may have a defective electrical component relative to the current track.