As an experiment, I plugged the Apple Pencil into my iPhone 6 Plus for 10 minutes. Apple Pencil charge went for 70% to 99% in 10 minutes. The iPhone's charge started at 100% when I plugged the Apple Pencil into it and was still at 100% when I unplugged it. I thought the iPad pro was the only device that can charge the Apple Pencil. Live and learn, I guess.