I'd use a sacrifical cable as a test.
I want to use the NW-HD5 as a little portable HD to copy photos from my camera too when out and about. I've got a Sharkoon USB bridge that lets me connect the HD5 on one side and my camera to the other and it copies all the files across. No need for a computer so perfect for shooting RAWs.
The problem is, every time I plug in the HD5 it starts trying to recharge and quickly drains the Sharkoons batteries. Is it possible to somehow disable the USB charging on the HD5?