Erick Ruiz de Chavez

Energy Shields at Minimum: Automating Laptop Power Mode

Published: 2024-12-29

I love automation—not just home automation but anything that simplifies my life. For example, I use a Shortcut on my iPhone that automatically turns on Low Power Mode when the battery drops below a certain percentage.

This morning, while working on my laptop, I realized that macOS allows Low Power Mode to be set to "always on" when on battery power, but it doesn't provide an option like "only when the battery level is below X%." Naturally, I decided to create a script to achieve the same functionality on my laptop that I already enjoy on my phone.

After a quick search, I found the commands needed to set the power mode and check the battery level. Another search revealed that macOS supports allowing specific users to execute scripts with sudo privileges without needing a password. 💥 A few minutes later, I had my laptop automatically enabling or disabling Low Power Mode based on the battery percentage. 🤓

Here's how you can achieve the same result.

Step 1: Create the Script

First, create a script to check the current battery level and set the Low Power Mode accordingly. I like to save my scripts in $HOME/bin. On my laptop, that's /Users/Erick/bin. So, I created a script at /Users/Erick/bin/low-power-mode with the following contents:

#!/usr/bin/env bash

# Get the current battery level
_level=$(pmset -g batt | grep "InternalBattery" | awk -F '[\t;]' '{print $2}')

# Remove "%" symbol from the battery level
_level=${_level/\%/}

# Get the current Low Power Mode state
_current_mode=$(pmset -g | grep lowpowermode | awk '{print $2}')

# Initialize the new mode variable
_new_mode=

# Enable Low Power Mode if the battery level is <= 10%
if [ $_level -le 10 ]; then
    _new_mode=1

# Disable Low Power Mode if the battery level is >= 25%
elif [ $_level -ge 25 ]; then
    _new_mode=0

fi

# Update the Low Power Mode state if it differs from the current state
if [ "$_current_mode" != "$_new_mode" ]; then
    pmset -a lowpowermode $_new_mode
fi

Step 2: Make the Script Executable

Make your script executable with the following command:

chmod +x /Users/Erick/bin/low-power-mode

Step 3: Allow Passwordless Execution

The pmset command requires root privileges, and since the script will run automatically, it needs to execute without prompting for a password. To achieve this, update the sudoers file:

Open the sudoers file with the following command:

sudo visudo

Find a line near the end of the file that looks like this:

%admin      ALL = (ALL) ALL

Add the following line immediately after it:

%admin      ALL = (ALL) NOPASSWD:/Users/Erick/bin/low-power-mode

Save and exit (in Vim, use :x⏎).

Step 4: Automate with Cron

To run the script automatically, schedule it using cron:

Open your crontab file:

crontab -e

Add the following line to run the script every minute:

* * * * * sudo /Users/Erick/bin/low-power-mode

Save and exit (in Vim, use :x⏎).

And That's It!