I have a 14000 mAh waterproof pack from New Trent, that I don't think is being made any more. I'm often Out There map-making, and on those trips I'm running GPS to record track logs pretty much whenever I'm in motion. I find that my Samsung phone will last a day's hiking if I turn off all the nonessential features (especially, running it in "airplane mode") and don't use the screen too much (the backlight is also a battery hog). The 14000 mAh pack has let me be out there for six days at a crack running that way.
This device is by far my heaviest 'luxury item,' but it fuels part of what I'm out there to do.
For me, it was worth springing for a waterproof one. Don't bother about the ones with solar cells, the solar cells don't really generate enough to keep you running. I just recharge in town.