#!/usr/bin/bash
export DISPLAY=:0
CAPACITY=$(cat /sys/class/power_supply/BAT0/capacity)

# perform notifications
if [[ $CAPACITY -lt 20 ]]
then
    MSG="Battery low: $CAPACITY%";
    /usr/bin/notify-send "$MSG";
fi

# suspend system when battery is low
if [[ $CAPACITY -ge 0 && $CAPACITY -lt 10 ]]
then
    MSG="Should suspend now, battery critical: $CAPACITY";
    /usr/bin/notify-send "$MSG";
fi