My phone loses battery when it's locked.

[Samsung4Ever]

Hello. I have a Samsung Galaxy Young, and it's causing a problem.

I shut it off at night, maybe around 11:00 or 10:00. It was at a 100%, and when I woke up and checked at around 7:00, it had almost 40% charge.

Can anyone help me? Does anyone know how to solve this?

 

[Samsung4Ever]

I meant that it loses battery life when it's OFF. It also loses battery when it's locked, something my old Samsung didn't do. I'm expecting it's because some app is running unnecessarily overnight. I'm not sure, so please give suggestions.