low-battery-notification.sh

#!/bin/sh
while true;
do
    # Minimum battery level in percentage.
    # If remaning battery percentage is less than this then a notification will be shown.
    MINIMUM_LEVEL=23;

    # Determine battery status
    BATTERY_STATUS=$(upower -i /org/freedesktop/UPower/devices/battery_BAT0 | grep -E "state" | sed  -E 's/state://' | sed 's/^[ \t]*//;s/[ \t]*$//');

    # Calculate remaining battery
    REMAING_BATTERY=$(upower -i /org/freedesktop/UPower/devices/battery_BAT0 | grep -E "percentage"|sed -r 's/([^0-9]*([0-9]*)){1}.*/\2/');

    if [ "$BATTERY_STATUS" = "discharging" ]
    then
        if [ $REMAING_BATTERY -lt $MINIMUM_LEVEL ]
        then
            # Send a notification
            notify-send -u critical 'Low Battery' $REMAING_BATTERY' % battery is remaining. Please plug your charger.';
        fi
    fi
    # Sleep for 45 seconds and then recheck
    sleep 45;
done;