I find myself often low on phone battery and wanting to use my laptop somewhat on a trip without a plug on an airplane. Here is a quick tip to charge your iPhone from the laptop without using much battery.
1. Open your MacBook Pro to the point it wakes from sleep.
2. Plug in your iPhone and the usb cable to start charging it.
3. Put the MacBook back to sleep.
4. You’ll notice the iPhone continues to charge off the laptop while its sleeping. Heaven.
By the time you land your iPhone is back to 100% charge and you sipped just a bit off your MacBook Pro.