The label on the Phantom 3 battery packs shows a nominal voltage of 15.2 volts. I decided to check the voltage on three packs - all were freshly charged with the stock charger and the charging hub. Using two different Fluke DVMs I get 17.1 - 17.2 volts off the main connector. Now these are packs that have had no real load on them (just whatever it takes to start the blinkies). Any thoughts?

Nominal voltage is about midway between fully charged and fully discharged and varies with battery chemistry. You can Google this for more detail.

Nominal Voltage is a voltage with which you define a typical battery. It's halfway between fully charged and discharged levels. It came from the fact that terminal voltage keeps changing with load and time and how do we calculate energy delivered. A nominal voltage is defined to do this computation. A 15.2 v battery at 1 amp load will deliver 15.2 WattHour in one hour on average. P3 battery has 4480 AmpHr rating at 15.2Volts. That means one can draw 4.48*15.2= 68 Watts for an hour. We can make many calculations with these numbers. For example an average current drawn by a motor if battery life is 25 minutes: 68 * 60/25 /15.2 / 4 = 2.68 Amps on average per motor