Keeping the phone on airplane greatly reduces battery drain. Get a solar phone charger. They're fairly cheap and work well, assuming you have some sunshine. I have a 20k battery pack that will recharge my phone several times. Use both a battery pack and a solar charger to recharge the pack in camp during the day. Then you can recharge the phone from the pack at night so you don't have to carry the charger with you all day. Also, hire a porter to haul all this stuff to your camp.
Agree, in airplane mode battery life is amazing. I also have a cheapo solar charger that works pretty well for $20. Of course, we got good sun here.
If you run OnX to mark your trail, it will use some battery, as will anything else. I seldom do that.
