After some days, I think that I can make same conclusion. Battery really need to be charged and discharged for a few times. Now I believe that everything is OK. I switch off manually my reader when I don't use it, and battery capacity is satisfying now. There is a very good explanation on web address:
http://faq.icarusreader.com/index.ph...hlight=battery
and
http://faq.icarusreader.com/index.ph...=87&artlang=en
Icarus is the same hardware as onyx boox and it will be nice that ONYX put similar instruction in their manual.
Once again, thanks to everyone who tried to help me.