While the apeal is there to take the smartphone as your only line of commo and mapping to the back country, I would still take a paper map and compass as well as the dedicated GPS. Think about it like this, most smartphones get their GPS ability from triangulating off the cell towers to give you your location (not sure if this has changed or not)... so what happens when you are out of cell coverage? Is yours like that, I dont know... however, a simple test is to go to an area that has no cell coverage and fire up the GPS part of your phone, see how it does. Unless you download and save offline maps before you leave coverage, you will end up with a blank screen showing your icon for your location, unless you are in the tundra, you dont want to see a white screen.
I have the Casio Commando 4G LTE, and I bought the extended life battery, with that and the GPS and screen on all day, I can get 6-8 hours out of my battery, cut that in half for the stock battery it comes with, if I run anything else, that drops down quite a bit. Another way to test your battery life in a controled enviorment is to turn it on and run the mapping/GPS app you are planning on throughout a normal day around home or the office looking at it and following it as you would be in the back country, this will give you a good idea of how long to expect your battery to live in those conditions.
So lets see I will run down your list...
Battery Life -
Airplane mode- shuts off all radio signals including GPS. while it will extend your battery life, it shuts you down to everything else signal wise.
Solar charging- on a recnt camping trip, a friend brought one of those solor chargers and it took a good couple hours (4 or so I think) to charge his phone from about 5% back to 100%
Other charging devices- I have one of those portable batteries, small tube like thing, never had to charge my phone with it yet, so I can't say how well it does, but you are supposed to be able to fully charge your phone off it a few times before it needs to be recharged.
Phone Damage - Water. Drops. Scratches. Losing phone. I keep my phone naked (no case or screen protector) Maybe that's a bad idea if I plan on taking my phone backpacking!
I would plan on either leaving it in a safe place in your pack or get a case... My phone is designed with the elements and more in mind, so I take mine naked without fear.
Upon a lil digging,
http://www.phonearena.com/phones/Samsung-Galaxy-S5_id8202 says you have IP67 certification for water and dust.
Mapping App - Too many to choose from (I'll probably create a separate thread for help in choosing one). I hear the smart phone GPS receivers aren't as good as dedicated ones.
Most smart phone GPS recevers are a patch antenna, so for best results, face the screen flat up in your hand towards that sky... accuracy is decent enough, comaprable to the early models like the Yellow Garmin eTrex. As per the link, you also apear to have a stand alone GPS, so you will get location targeting even without a signal. If you know an area where you do not get a cell signal were you can hike at least a mile or so, i would take a trip out there and test it.
As to apps, I use a few depending on where I am going and what I am doing. For street navigation, I prefer WAZE, for anything else, I have US Topo Maps, Bike Activity, and Wikiloc. Being as my phone is a G'zone phone, I also have G'zGear and G'zWorld. G'zWorld looks promising as soon as I figure out how to use it.
Photography - I'm mostly a point and shooter but still I think I'd miss some of the features of my camera. But some of these smart phone cameras take some pretty sweet pictures and have some cool features as well.
As to photographs, I just use the stock software it came with, it works for me and what lil I take pics of with it.
Has anyone fully embraced the smart phone only method?
Any tips or advice?
Get a case if you are gonna take it into the elements, your phone will thank you.... Test your battery life under conditions you are planning to use it as when in the back country while still here in the front country.
Anything I'm overlooking?
Nothing I can think of... there is so much they are capable of, there will always be something overlooked.
Other uses?
There are a million and one other uses, just depends on how the tool is used and fit into your life.
Downsides?
The more you run at the same time, the faster the battery will drain and shorten its usefulness. Everything is a compromise, the smartphone is not best at any one thing, but it is ok at most things you will use it for.
