Thanks for very detailed answer. Yes, I was thinking only about keyboard with wi-fi dongle. I've already noticed that unfortunately bluetooth will not work. There is a rather small range of portable USB keyboards that are specially dedicated to android devices. I was looking for one with a stand for comfortable typing anywhere I will be... a train, park bench etc.... Or well, you can find many usb keyboards with stands on ebay for example , but they all looks almost the same just with different logos, cheap, poor quality ones. Market is concentrated on bluetooth keyboards, then a lot of them are quite decent. So I'm just going to find a good usb compact keyboard, and then mount some kind of stand to it myself. Anyway, that is not very important for others, this post might be already to long.
ok, my question is: will it help to reduce battery usage in usb host mode, if I'll use keyboard powered by batteries?
Excuse my English. Thanks