Thats about the same thing that happened to me.. I was doing homework and i using my tablet for research and for some tunes, when it got to 4%. So i plugged it in thinking it was charging. I went to go back on and it was 3%. I was really confused so i restarted it and plugged it back in. Still, nothing. The next day i went and took it back and got a new one. I actually got 22.00 left over.
I had this issue for quite some time. I called samsung and they didn't believe me but finally agree to look at it. But now it hasn't done it in 3 days. Wtf. Lol why them not change anything. Wonder if I should just keep it. I was trying to get a video of the issue.
edit: sending it back. the battery just jumped from 49 to 100%. that can't be right..
Sent from my Nexus 5 using xda app-developers app