I've experimented a bit more with the YoGen and I have good news. I was able to get some response from the N900 by setting the YoGen to the higher voltage setting (there's a little switch) and turning the N900 off completely. When I did that, I was able to get the green charging light on the YoGen to flash on and off, and the orange charging light on the N900 to pulse. I haven't yet run down my N900 battery to empty and then attempted to spend a half-hour pulling to see if it's really charging though.