net.mxey.homebrew.upgrade.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>Label</key>
	<string>net.mxey.homebrew.upgrade</string>
	<key>ProgramArguments</key>
	<array>
		<string>/Users/mxey/bin/upgrade-homebrew-on-ac</string>
	</array>
	<key>StartInterval</key>
	<integer>46800</integer>
</dict>
</plist>

upgrade-homebrew-on-ac

#!/bin/zsh -e

if system_profiler SPPowerDataType | fgrep -q "Connected: No"; then 
  echo On battery power, not running
  exit 0
fi

terminal-notifier -message "Upgrading your Homebrew packages"

if brew update && brew upgrade && brew cleanup; then
  terminal-notifier -message "Homebrew was upgraded"
else
  terminal-notifier -message "Homebrew upgrades failed"
fi%