I think this is another place where an old adage applies: "It's how you use it".

When I use a dedicated GPS, i.e., a device sold as and intended solely to function as a GPS, I almost never just turn it on and leave it on. There ARE situations where that makes sense, assuming I'm confident that I have battery power to burn. But my normal use is to turn it on, get a fix, then turn it off.

Ditto with smartphone. In this case "turn it on" means to turn on the GPS hardware, bring up the app and do whatever you're going to do, then turn the GPS hardware back off. In general, any wireless service is somewhat of a battery hog, whether GPS, blutooth, or phone.

If a person gets serious about using a smartphone as a sort of "swiss army knife" of functionality in the backcountry, it's well worth while to take some time to learn about conserving battery life. An internet search along the line of "smartphone battery life android" (or iphone or whatever) will turn up a lot of stuff. "How you use it" can make a very large difference in conserving battery. I use my phone on backpacking trips as daily blogging device, my only camera, I occasonally read books on it, use it as a voice recorder, infrequently check weather reports and email/facebook when in range of cell towers ... and use it as a GPS once in a while too. Battery life is never a problem, though I sometimes do carry a spare battery, depending on the trip.