Present a battery alarm banner in sway and shutdown computer if battery is lower than 2 percent

swaybat.service

[Unit]
Description=Sway battery alarm

[Service]
ExecStart="/usr/bin/dash" "/usr/bin/swaybat"

swaybat.sh

#!/usr/bin/dash

read -r status < /sys/class/power_supply/BAT0/status
if [ "$status" = "Charging" ]
then
  exit 0
fi

read -r energy_full < /sys/class/power_supply/BAT0/energy_full
read -r energy_now < /sys/class/power_supply/BAT0/energy_now

charge=$(/usr/bin/dc -e "10 k 100 $energy_full / $energy_now * 0 k 1 / p")
if [ "$charge" -lt 2 ]
then
  /usr/bin/systemctl poweroff
elif [ "$charge" -lt 11 ]
then
  /usr/bin/swaynag -m "Battery low ($charge). Please charge now."
fi

swaybat.timer

[Unit]
Description=Sway battery alarm

[Timer]
OnBootSec=1min
OnUnitActiveSec=1min

[Install]
WantedBy=timers.target