Here's the thing: you may find some place to backpack where you have cell service. Maybe. But good luck with that.

I have an external battery - a Brunton - that I have used to charge my camera as well as my phone on a longer trip. But I use the Kindle app on the phone, and store a number of leisure reading books as well as a NOLS wilderness medicine book, and was at the time reviewing this GPS app on the phone so needed that to continue working. At no point did I even get reception on the phone. I've been in maybe two parks where there was half a bar on the phone - that wasn't even enough reception to call anyone.

In the past four years of search and rescue volunteering there has been one instance of someone being able to contact us by phone. They had injured a knee within a mile of the trailhead near a popular resort town on the shores of a popular lake. That was a total fluke of chance.

So before you base your purchase on the premise of calling all your friends from the trail, figure out if there's actually going to be cell service there so you aren't totally disappointed.