Page 34 of the Mavic Mini manual says that Cellular data is required when using the DJI Fly app. Is this true and if so is there a way around it?? also how long should IPhone battery last while connected to the controller. I started with a full charge and by the time I got everything set up and ready to try to fly the phone battery was down to 10% and Mini wouldn't start. I have very marginal cell signal here at best. TIA