2004 Lariat with tow package, 1 year old best Sears battery available and about 131,000 miles. I have a radar detector that shows the voltage on the display. It's always shown about 14.4 volts all the time when the engine is running. Lately, it's only showing 13.6 or so. You think the alternator is getting weak? I haven't noticed any real problems, but I thought it was odd that the voltage is showing around 13.6 now when in the past it always showed 14.4

 

I would just keep an eye on it and if it starts going lower, down to about 13.0, then I would get the both the battery and altenator checked out. Also, take a look at the battery terminals, they may need cleaning.

 

I believe if you go back to Sears Auto, they will test the battery and charging system for you. 13.6 is too low, either something is wrong or your radar detector is reporting voltage incorrectly. If you have a multimeter, try to confirm the reading across the battery terminals themselves. While under the hood, check the terminals for corrosion.