Install some app and you see it drop. For now my advice is to uninstall all apps you can and then some. There is also a chance the battery has begun to fail early. Ask your carrier if they can test that phone for early battery failure.
The battery on my phone drains so fast that it reaches 50% within four hours. (connected to WIFI not 4G)
I'm using it only to make phone calls as of right now. When I use it to watch video or access 4G it will give even lower rate. I've had the phone from AT&T around 40 days ago. I checked the battery graph and there is a sudden drop from 100% to 84% within the first 15 minutes after I unplug it.
Charging is taking around 6 hours to fully charge.
The phone does not last me the whole day without recharging it constantly.
Any feedback would be highly appreciated.