Hi Alex,
You probably already know this, but for the GPS to work the iPhone must have the cellular function active (no airplane mode). Since most of this route will not have cell phone coverage the phone is constantly searching for service, and this tends to consume the battery. If you do not already have one I suggest a mophie case (or similar) with extra battery. I had a great "first timers" experience with the MR one year ago, so I think I understand "where you are". I'll be very interested in reading your trip report. Also, good to hear that you are undertaking this hike with a friend. Good to have a sounding board as you decide which way to go.
Good luck - both with the weather, and on the hike.
John
