Log out users when laptop battery level gets too low

battery_level.sh

#!/bin/bash
# Cronjobs for each user can be edited with "crontab -e"

battery_level=$(cat /sys/class/power_supply/BAT0/capacity)

battery_level_threshold=35

if (( $battery_level > $battery_level_threshold )); then
    echo $(date -u) ": Battery level ok:" $battery_level"%"
    exit 0
fi

ac_power_present=$(cat /sys/class/power_supply/AC/online)
if ((ac_power_present == 1));then
    echo $(date -u) ": AC-power present"
    exit 0
fi

export DISPLAY=$(whoami)
export XAUTHORITY=/home/$(whoami)/.Xauthority
export XDG_RUNTIME_DIR=/run/user/$(id -u $(whoami))

/usr/bin/notify-send 'Laptopbatterij opladen nu!'
sleep 3
# Users still have the option here to cancel the logout
gnome-session-quit --logout

#Punishment when battery level is too low and power adapter not connected.  No more cancel option.
#killall firefox