SHELL: Battery script to make sure overcharging doesn't happen

battery.sh

#http://askubuntu.com/questions/518928/how-to-write-a-script-to-listen-to-battery-status-and-alert-me-when-its-above 
#!/bin/bash
    notify-send "Battery monitoring enabled"
    while true
    do
        export DISPLAY=:0.0
        battery_level=`acpi -b | grep -P -o '[0-9]+(?=%)'`
        if on_ac_power; then
            if [ $battery_level -ge 90 ]; then
                notify-send "Battery charging above 90%. Please unplug your AC adapter!" "Charging: ${battery_level}% "
                sleep 20
                if on_ac_power; then
                    gnome-screensaver-command -l   ## lock the screen if you don't unplug AC adapter after 20 seconds
                fi
             fi
        else
             if [ $battery_level -le 15 ]; then
                notify-send "Battery is lower 15%. Need to charging! Please plug your AC adapter." "Charging: ${battery_level}%"
                sleep 20
                if ! on_ac_power; then
                    gnome-screensaver-command -l   ## lock the screen if you don't plug AC adapter after 20 seconds
                fi
             fi
        fi

        sleep 300 # 300 seconds or 5 minutes
    done