Low power mode for Macs

local.droopy.lowpowermode.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>local.droopy.lowpowermode</string>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/bin/osascript</string>
        <string>/Users/suranap/.local/scripts/LowPowerMode.scpt</string>
    </array>
    <key>StartInterval</key>
    <integer>1200</integer>
</dict>
</plist>

LowPowerMode.applescript

-- Check the battery level
set batteryLevel to do shell script "pmset -g batt | grep -Eo \"\\d+%\" | cut -d \"%\" -f 1"
set onBattery to do shell script "pmset -g batt | grep -q \"Battery Power\" && echo 1 || echo 0"
set onLowPowerMode to do shell script "pmset -g | grep lowpowermode | grep -o \"[0-9]*\" "

if onLowPowerMode = "0" and batteryLevel < 20 then
	do shell script "pmset -a lowpowermode 1" with administrator privileges
else if onLowPowerMode = "1" and (batteryLevel > 80 or onBattery = "0") then
	do shell script "pmset -a lowpowermode 0" with administrator privileges
end if

To install:

1. Paste AppleScript code into Script Editor. Save somewhere.
2. Copy plist file to /Library/LaunchDaemons under some name
3. Change label on line 6
4. sudo launchctl start <your plist file>