06 f150 5.4 3v. 168k. Stock. Not sure if alt. Or batt is issue But recently when starting after work I've seen twice the battery gauge lower that it be should be. Both times I forgot to check when I got home with a DVM. I put a napa battery in it two years ago. Within a year the battery slowly lost alot of cranking amps. It was warrantied. It's been less than a year. Today it cranked slow and the battery guage was reading high when it started. Again didn't check. I talked to Napa. They will warranty for me but b at some point they will stop. The one guy stated that vehicles after 04 had to be reset with a high end scan tools when replacing the battery. He said they PCM changes the alt output based on battery age. I've never heard of this. I always thought the altenator's voltage regulator controlled it's own output. Anyone know of this on this generation? Anyone have a truck slowly eat battery's? Thinking of replacing alt abut not sure I should if there's something in the PCM to try first. Will do voltage drop at starter to check wiring with new battery. And parallel dvm test to check alt wiring. I'm very good at electrical. But I think I'm getting a line of BS so tothe don't have to warranty anymore. Thoughts?

 

I'd want to look for a "phantom" or parasitic load. Modern vehicles don't completely shut down for as much as an hour, the various modules stay energized and draw a fair amount of juice. But if there's a problem they can present a constant low level drain. If you drive it regularly it might not even get noticed except that the battery doesn't last very long.

 

Should be getting 14.2 volts at the battery at idle if your alt is working good. You can test for a parasitic load by opening hood, waiting for everything to shut down-lights ect and testing for a drain. I'm on my third battery on my 06 and never had the PCM reset, that is bs. Check alt wiring and voltage at idle, if good and no draw when everything is off, then it most likely is a bad battery. My mom's escape was eating batteries and it turned out to be a internal short on the remote start.

 

But I think I'm getting a line of BS ( on resestting the PCM) so they don't have to warranty anymore. Thoughts? --BINGO.

 

There is a alt warning circuit but no control, its all from the voltage regulator . This monitor circuit is why when changing alt, pcm displays a false battery alarm . That is why its so hard to find a good rebuilt alt . We have never deeply investigated that monitor circuit .

 

Full battery management did not begin until after 2006.
You have to do the testing to uncover a Drain and or an underperforming alternator.
Until then is just guessing.
At least put a voltmeter at the battery, start the engine and look at the voltmeter.
It should have gone to at lest 15 volts if the alternator is outputting, then taper off as the battery recovers its charge, then settle at about 14 volts..
For drain you can put a small bulb in series with the positive cable.
Depending on its size should light up from a Drain.
Then remove/replace one fuses one at a time until you see the lamp go out.
Remove the under hood lamp and close all doors.
One item to remember is the Alternator has a Diode stack. If that stack has a faulty diode it will place a drain on the battery after shut down but still charge when engine is running.
The way to test for this is remove the heavy cable on the alternator then touch it back to the stud. If you see any spark there is a drain from the diode stack. That means the alternator has to be replaced.
You have to do the testing to find the issue.
Good luck.