Sorry for bringing this up, but I'm seeing the same behavior sometimes in my Moto X. And I bought it 3 days ago too. I did a topic yesterday. Its like sometimes (not always) it suddenly rises up like 2 o 3% by itself and then it sudden drop that same amount. I can see these little spikes in the battery stats, however, I noticed it 2 or 3 times. Thing is, I'm quite obsessive so I did see how it sudden went from 50 to 53% and then I saw that 3% drop later on.. Its not that I'm always looking at the battery but I have the numbers in my status bar and I use to check them out (and rememer them) every time i pick up the phone lol.
The temperature is really hot down here right now, maybe that's contributing. I hope after more days of use and charges it gets normal.