IPhone 5 dead every time I wake up?

Okay so these past 3 days I've been going to bed with my phone on like 80% or a little less, and I've been waking up with it dead:/ any ideas of what might be going on?

Not charging it overnight?

Maybe you have a lot of apps, apps kill your phone fast too. Also, if you charge your phone a lot and keep it in even though its already charged, it can mess up your battery and talking on the phone while its charging messes up the battery too.