My voltage goes from 12 volts or lower like to 11 then hangs a 14 volts or 14.5 voltage. It only does it when the truck is warming up.

 

That is most likely the grid heater(s) cycling. Quite normal for a cold truck just started and warming up.

 

it never has done that before. How could I fix it?

 

Tell Texas to not get so cold?


Seriously, it's very normal for the grid heaters to cycle initially during cold weather . It is not broken, you don't need new batteries. You might consider reviewing the owner's manual to learn more about how and when they work.