I got the second battery charged far enough that it's recognized by the Duo 250, and it's charging further in the Dock now.

Strangely, the first battery when "fully" charged will run the Duo 230 for about 15 minutes, but the Duo 250 won't even turn on with that battery. Not even a peep out of it when I press the power button while using that battery. So I've never seen this lovely Duo 250 screen, since I've only been able to run it inside the Dock.