I have the CLIE PEG-NX70V, which is the next model up from the NR. It does not charge in the cradle alone without the power cord attached to the cradle. I can sync it through the USB without charging up the battery when it's disconnected. (In order to extend my battery life, I purposely tried to use the unit down to <20% before charging).
I don't know if this is exactly the same case as the NR, but they are very similar units. Hope this helps.