Never thought I would, but I've been using ViewRanger for a couple years and I love it! Signed up for it for free then paid $16 for a lifetime subscription to be able to download maps to use in the backcountry, when there's no cell/internet coverage. It tracks me on the maps, tells me how far I walked, how much elevation gain and loss, has a peak identifier (not the best one I've ever seen) and lots of other features that I don't understand.

When off trail, the tracking shows were I am which especially helpful when I'm trying to find my way back or trying to get to a certain spot.

As far as keeping the phone charged, I recently acquired an Anker, PowerCore 13000 for recharging. On a recent Wind River trip of 7 nights, the charger kept my phone and my buddy's charged the whole time. I think that's saying a lot when you take into account that my phone is tracking most of the time and it is my only camera. I took a lot of photos and a number of videos.

It weighs 8oz and cost roughly $30, I think.

And no, I don't sell them or work for them, just think it's an amazing product.