I am using a MacBook and the battery is unreliable. I am trying to find a script command that will enable the laptop to play a beep when the battery level is lower than a threshold. After some search and tests, I found a quick solution below:

1) I first create a file called check_battery with the following contents:

ioreg -l | awk '$3~/Capacity/{c[$3]=$5}END{OFMT="%.3f";max=c["\"MaxCapacity\""]; bat= (max>0?100*c["\"CurrentCapacity\""]/max:"?"); printf("%d", bat)}'

2) I then created the following file:

\#!/bin/bash
sh check_battery>battery;
let t=60
read a < battery
if(( "$a" < "$t" ));
  then
  say "Battery level is lower than 60%!";
  say "BEAP BEAP"
fi;

3) Finally, I try to add it to my crontab job, but crontab has been stopped by iOS. Then I found that I have to use launchd, which is detailed below: https://alvinalexander.com/mac-os-x/mac-osx-startup-crontab-launchd-jobs

It is now working at my MacBook labtop but there may be better solutions. Do share with me if you have other solutions. Many thanks.