Why does my phone's screen go black randomly?

[coconut boi]

Hello I have had a LG phoenix 4 for about 7 months. I find that fairly new it is not damaged and I even bought a glass screen protector and silicon case to protect it. Anyways so recently about 2-3 months ago I noticed that when ever I'm using the phone the screen just goes black, it happens the most when I click the off button on the back and then turn the screen back on however when I do so the screen is black, the phone itself is still on but the screen is just dark. Not sure if this is caused because i turn it on and off too fast. Although the phone is on I still receive messages the screen is completely black and i can't see anything not even the option to shut down or restart my device. So I always end up taking out the battery and turning it back on and it works the screen is no longer black. I noticed this happens when the battery is around 20%-50%. What could be causing this issue is it an expensive fix? I mean this phone is cool and all but the phone itself is a cheap 50 dollar prepaid burner phone and I yaint spending more than the phone's actual value to fix it. Might as well buy a new one if I'm spending 50 or more to fix my old phone. Kinda of a broke as over here.

 

[B. Diddy]

Welcome to Android Central! Does this also happen in Safe Mode? www.att.com/devicehowto/tutorial.html#!/stepbystep/id/stepbystep_KM1320238?make=LG&model=LGLMX210APM

Since it's only 7 months old, it should still be covered by warranty, in case it comes down to that.