chromebook shuts off randomly on battery power

[flandere]

My HP Chromebook 14 G3 shuts off randomly while on battery power, but only when using Gentoo, not when using ChromeOS.

The problem goes away when plugged into AC power.
It usually takes a while before it happens. The shortest time I've seen is ~6 minutes, usually it takes about half an hour, the longest I've observed is 4 hours.
It only happens when the battery charge is lower than 80%.
This happens when I'm actively using the machine, for example playing videos with mpv or editing files with vim.
This also happens when not actively using the machine.
This happened with only a stage3 tarball, nothing else emerged.
This still happens with X11 + lightdm + i3.

I'm at a loss for what to do, I've tried different chromiumos kernels, laptop_mode_tools and comparing configs in /etc between ChromeOS and Gentoo.

dmesg(from Gentoo): http://pastebin.com/yzLiTisp

Any advice would be greatly appreciated!