I am, admittedly, completely wandering in the mist when it comes to knowing all about phones, or technology of any kind. I use the stuff, but boy, I do not understand it much. I was concerned about the battery life of my phone (T-Mobile 1+ 6T) when I purchased a Zoleo emergency device, because it depends on your phone to type and receive messages. And with a new software update from Zoleo, it now draws on my phone more often to check messages and keep the app working. Grrr.
My daughter, bless her, pointed out how important it was to put the phone on battery saver mode, and I used that during our hike on the Camino Primitive in Spain...but still wanted to use data, etc. So my battery was down to 50% by the end of the day--8-10 hours later. And that's without the Zoleo.
On this last trip into Desolation Wilderness, I decided to see exactly how carefully I could manage my phone battery. I took along the Zoleo, and also an emergency battery pack, just in case. At the trailhead I had a fully charged phone, the battery pack, and the Zoleo. I turned the phone to battery saver and airplane mode. I did not turn on the Zoleo--figuring that in any backcountry emergency, the minute it would take to turn on the Zoleo and connect up would not be a question of life or death. And I stuck the battery pack in my pack and let it sit there.
After one day on the trail, leaving the phone on but only using it to take photos, I had 91% of the battery left. That seemed too good to be true, but I turned off the phone (stuck it in the pocket of my sleeping bag so it didn't get too cold) and didn't turn it on again until I was ready to take the next photo the following day. At that end of that day, the battery was still at 81%
Same procedure, and the end of the third day left me with 73%, until I took a few minutes to show my wife all the photos I had taken.
By the end of the hike, I had used the phone for four days, probably a total of 25-30 hours, just to take photos, and the battery was at 62% when I got back to the car. Pretty darn good. I never did turn on the Zoleo, because we never did get into a situation where we needed it. But if I had, I would still have had plenty of phone battery, and the extra battery pack, to manage.