Actually, The Fine Manual stays start at something above 50%. It's not always practical to start with a full battery and if DJI says 50%, they ought to engineer it so it can safely fly at 50%. .....
My main takeaway from this discussion is to always start with a fully charged battery. That said, I think DJI has missed the mark in programming their software (firmware) to shut off the motors at some critical battery voltage. It would make far more sense, when reaching that "critical" limit, to 1) Put an alert right across the app screen; and 2) Begin a soft landing protocol, allowing you some leeway to maneuver to bring your bird down safely. How about it, DJI?
