Alert messages in case of low charge level

batteryAlert.sh

#!/bin/bash


file="/sys/class/power_supply/BAT0/capacity"

while IFS= read -r line
do
	if [[ "$line" -le 10 ]]
	then 
		notify-send -u critical "CRITICAL CHARGE LEVEL (10%)"
	else
		exit
	fi
done < "$file"

If you want to schedule this script to be run every certain amount of time, use the following command (example for every 5 minutes):

watch -n 300 ./batteryAlert.sh