When you don't use all benefits, like cortana, iris scanner and skype, i think the battery lasts whole day. My lumia is right now 36h without charging and has 29%. But right now it is morning time in my country, so i can't get another day i guess. But yes, there is also heavy users and they get maximum 5-8h. I don't know what the hell they are doing. Some kind of battery torture tests i guess..
This is nice phone, beautiful screen, good voice quality, and yes - you are supported at least two years of constant new updates. My S5 mini did not get any updates the time i used this phone. (6 months)