If you have never done a battery calibration, you should try one. Rooted users can fully charge their phone and delete the batterystats.bin from /data/system. Then re-start the phone and let the battery run down to 5% or so, then fully recharge it. For stock users, there are apps in Play (market) that you can use without being rooted, but some get poor reviews due to intrusive ads. I suppose you could install one, calibrate, and delete the app.