I've had the phone for two years, and the battery tends to run out when it's halfway. And when I turn the phone back on, it'll pop up at 19%. Does anyone know the issue about that?
It might be time to replace the battery. My phone (SPH-D710) was doing the same exact thing and when I purchased two new batteries this was no longer an issue. Amazon has replacement batteries that should work. If you can find another brand (I bought Anker) see how the reviews are and considering going with that.
Battery life will slowly degrade over time. Two years is enough time to see poor battery life if you are still on the stock battery.