What happens is the screen is staying on even though it is black. So it drains a ton of power while you are trying to charge. If your battery has run all the way down, you can still charge it for half an hour, boot (you will have maybe 10%), quick turn on airplane mode or some other low-power tweak and turn the screen off. Then you will charge up fine.
To fix charging while powered down, you have to be on stock lg firmware with stock lg bootloader/recovery. You can still be rooted though, and do tweaks like xposed. This is my current setup.
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