Not really sure what you were trying trying to run with a single powered USB port using that mini battery pack; the N800/N810 puts out about 200ma when in host mode, and for anything above that I would imagine something like that portable battery pack of yours would get drained quite quickly making it a bit of a strange solution.

To achieve your goal of a powered USB port though the idea I came up with was to create a power adapter/host mode cable that had a Female USB A port on one side, along with a jack for the standard N800/N810 AC power cord; then on the other side have the mini USB connector and another tiny DC connector to plug into the N800/N810 power jack. The idea is you only need the 1 power adapter to power both your USB device and keep the N800/N810 trickle charging at the same time.

Now, whether it's really worth while to build all that up, I don't know, as a powered Hub is a bit easier, but not quite as handy for carrying around...