Nope: "For both iOS and macOS, the new Photos scans quietly for objects and scenes, but because facial recognition is more computationally (and thus battery) intensive, both OSes let you know that face-interpretation only occurs when iOS devices and Mac laptops are plugged in and have sufficient charge. In iOS, it can happen in the background while the device is plugged in."

http://www.macworld.com/article/3092715/photography/hands-on...