help: LG G4 was on, then got warm and turned off

LG G4 was on and working fine, then I noticed the phone was getting warm. The screen now was the "initial cut-on screen" and was stuck on that screen. I laid the phone aside then pressed the power button and the screen showed "battery too low to turn on." Don't panic like I did...it will turn back on after re-charging the battery.

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