Battery draining overnight

[AC Question]

I have a Samsung Avant from Metro PCS (runs on T Mobile). It is less than a year old. Suddenly, within the past couple of weeks, the battery had been draining very rapidly. And at night, when it isn't even being used, it can have a 100% charge when I go to bed, and the next morning it is down to almost nothing. It often says the screen is the biggest use of the battery, but I'm not sure how that can be, if the screen is not in use. Not sure what if anything I can do...??