Strange problem in my Lg G2

Hello Guys

My lg g2 has a very strange problem !!
Every thing is operating normally in the phone till battery reachs 60%
Once it be 60% the screen stuck in black most of times
Knock feature doesn't wake up the device, also the power button
After pressing 10s times on power button and knocking on the screen sometimes open sometimes not.
It needs to be plugged in wall charger to operate semi normal (it works good in the charger but it do stuck for one or two times only)
I noticed that the screen is Lighting up but it shows black only no data at all
And some times gives black only.
I tried to restart my phone. It restarts normaly but the screen still black even lg logo didn't appear but it opens with black again.
The screen is working i can hear my touch sound ( swipe look, answering phone call, volume up and etc.)
All this happened only once the battery reachs 60%
My devise not rooted, i did hard and soft reset, connected the devise to lg pc suite
Nothing helped.

Do you have any ideas? Is it battery problem or cables or what?:mad: