[Q] LG G3 5.0, very hot, battery barely lasts a day on minimal use topic

Hi, my g3 has this problem where the battery seems to drain very fast on moderate to minimal use. When it's in use I use it for browsing the Internet and maybe Facebook, nothing too energy burning, yet it burns the battery like I'm using it for a demanding task. The battery usage has nothing unusual (I don't think) just 39% and the rest is split between tasks. What might be causing this? Since the start of typing this thread is gone from 25 percent to 8 percent, and is very hot again. What might be causing this?

LG G3 d855
16 gb
2gb ram
Android 5.0

Also has one other problem where there is 5gb being used in the misc section for 'system' is this normal? Because that's a large portion of the 16gb gone.

Thanks in advance.