The chart posted above is correct, but only for a fully charged, then disconnected and rested battery (overnight). That said, you can let the truck sit overnight and then you can take a reading that will be close - BUT you can't just pop the hood and stick a voltmeter on the battery. That wakes up the computers and will give you a big voltage drop, quickly.

*Disclaimer what I'm about to suggest can be done safely but would be easy to screw up.*

What you need to do is attach 2 wires to the battery terminals and run them outside of the hood, with it closed. Tape up the positive end and be careful that it doesn't get pinched in the hood when it closes!!! Then take a volt reading from these wires after the truck sits overnight, but make sure you don't have your key FOB on you, and don't open a door, or ... you'll wake up those computers. When done remove the wires.

 

work great, range is about 25 (edit) feet.