Script to play a warning when battery level is und

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.

I think your script is a good script in its own right, but could end up being quite resource-intensive when run regularly because it invokes a shell process plus two programs to acquire the information you're after.

In this instance, I think AppleScript has a couple of advantages of a shell script, largely thanks to osascript, which is the only program that needs to be executed to run an AppleScript, and it can do so without creating a shell process.

AppleScript to Retrieve Battery Info

Here's one such script that can retrieve information about your computer's battery, and issue warnings at appropriate times:

property threshold : 20 -- The level below which the script issues warnings
property verbose : false -- Report current battery level on every run
property file : "/tmp/battery.log" -- The path to the log file (from plist)


set eof of my file to 0

tell the battery()
    set warning_level to the warningLevel()
    if the warning_level = 1 then return check()
    warn about (warning_level - 1) * 5 with alert
end tell

# warn
#   Sends out a visible and audible warning with information about the
#   remaining charge (+level) on the battery.  Invoke without alert to have
#   the +level reported in the notification centre as a percentage.  Invoke 
#   with alert to have the +level reported in a pop-up alert dialog as an
#   estimation of the remaining battery time (in minutes), and which must be
#   dismissed by the user.
to warn about level without alert
    if not alert then display notification ¬
        ["Current battery level: ", level, "%"] as text ¬
        with title ["⚠️ Battery Warning"] sound name "Basso"

    say "Warning: battery low" using "Moira" pitch 127 ¬
        speaking rate 180 without waiting until completion

    if alert then display alert ["Warning: battery level is very low"] ¬
        message ["Estimated time remaining: " & level & " minutes"] ¬
        as critical giving up after 0
end warn

# battery()
#   Contains a script object that defines a number of convenience handlers that
#   retrieve information about the on-board power source
on battery()
    script
        use framework "IOKit"
        use scripting additions
        property warninglevels : ["None", "Early", "Final"]

        on warningLevel() -- A ten-minute warning indicator
            IOPSGetBatteryWarningLevel() of the current application
        end warningLevel

        on info()
            IOPSCopyPowerSourcesInfo() of the current application ¬
                as record
        end info

        to check()
            copy [it, |current capacity|, |is charging|] of ¬
                info() to [ps_info, percentage, charging]

            if the percentage ≤ threshold ¬
                and it is not charging ¬
                then warn about percentage ¬
                without alert

            if verbose then return display notification [¬
                "Percentage: ", percentage, linefeed, ¬
                "Charging: ", charging] as text ¬
                with title ["