"X seconds on battery" problem

I recently bought a Galaxy Note 10.1 (2014) -- after I opened it, I saw that charge level was %50+. While I was using it, it shut down; and I couldn't open it for a while. I plugged the charger and waited for a while, then it opened with again with %57 charge level. Now it is still charging but whenever I open Settings -> Battery part, it shows a graph and it says "18 seconds on battery" (I don't know why 18, I couldn't see an example on the web). Moreover, the applications it shows seems a bit weird. I see a "Phone" app where there is no visible phone app at the widgets and apps section, as I do not have 3G, or this is not a phone, it is natural. I don't know what is going on, may be someone can guess what is wrong with the battery part...