Do you ever get that annoying alert that your iPad is not charging when you plug it into your Mac? It's the result of the iPad's requirement for a high-power charging source. If you find the alert annoying, then there is a quick and easy way to turn it off.
Unlike most smaller mobile devices, the iPad needs a higher current (2.1A) to charge its larger battery. If your USB port only outputs at 0.5A or 1.5A, then you will see the "iPad Not Charging" alert. Most newer Macs provide at least one high-powered USB port to support the iPad. Consequently, this alert only occurs when you plug your iPad into a low-power USB port on your Mac or into an unpowered USB hub that's connected to your Mac.
It's not a big deal if the notification pops up on occasion, but it is super annoying for developers who are constantly plugging and unplugging their iPads for testing purposes. Craig Hockenberry published a handy tip on his blog for turning on and turning off this alert using a few short terminal commands.
To turn off the notification, open the Terminal app on your Mac and type or paste in the following two lines:
$ sudo defaults write com.apple.usbd NoiPadNotifications \ -bool YES
$ sudo killall usbd
As noted by Hockenberry, the usbd daemon will still run the next time you plug in your iPad, but you won't see the alert. If you want to turn the notification back on, just open Terminal again and type in the following line:
$ sudo defaults delete com.apple.usbd NoiPadNotifications
If you are curious about your USB ports and what power they output, then plug in your iOS device and open the System Profiler app by going to the Apple menu in the upper-left corner and choosing "About This Mac." Click on "More Info" and then "System Report."
You should see an entry in the left-hand column for USB under the Hardware section. Select that entry, and you can view the available current, required current and extra operating current for the connected device. Details on what these different values mean are explained in this Apple support document.