Voltage display vs battery voltage?

[70runner]

Noticed today 25 Rebel cluster voltage gauge showed 15.5v while driving, sometimes, when decelerating, dropping to 14v. No warning indicators. Got home, broke out the Fluke and measured 13.1v at battery terminals with ignition off. Truck parked, running, with A/C, lights, seat heater, and such 12.9v on Fluke while gauge shows 15.5v. Both batteries check good on Ancel BA101+. What think ye?

 

[Hanover Fiste]

The Fluke is probably more accurate than the cluster gauge. However, the cluster gauge might be measuring the voltage at another point, or another circuit.

 

[70runner]

From what I can gather from the interweb, apparently the cluster gauge rendition of voltage is some arrangement between the BCM and IBS modules. I stuck the Fluck on the alternator output post, the same ~13v measured at the battery with the truck running. At least I know the alternator isn't cooking the batteries.