On my last big trip in the Blue Range area I carried a LOT of electronic crap, and it's a halfway good thing I did.
First up was my rather antique Garmin eTrex Vista HCX. Aside from the paper maps and compass we had, this was to be the primary route tracker, nav tool, etc. That went out the window about 2 hours in when the batteries died. Odd, so I popped in another set of Eneloop AA's (everything was charged up before leaving home) and got about the same until those too died. Later determined that the cells were simply old and worn out and didn't hold any meaningful charge anymore. So out the window THAT plan went.
I had my phone with me though, as I like the maps and layers available in the Gaia app, so everything was pre-cached as a backup anyway. Samsung Galaxy S5 in airplane mode with GPS and bluetooth turned on, and a fairly bright screen setting, and it easily lasted the rest of that day and was getting extensive use (trail disappeared on us constantly) for both nav and satcoms via my linked Delorme InReach. (that bugger is fantastic btw.)
The phone then played music into the night at camp as drunken karaoke commenced to celebrate not dying. Got it down to about 30% and finally plugged it into this beast:
Similar to the Anker devices, but a little cheaper. I'd been using that battery pack around town day to day for months before and it didn't let me down. It managed to keep the S5 going for two more days plus the InReach (which also uses the same micro USB charging port) which was beaconing at the shortest interval (10 minutes) the entire time and burned through easily more than 200 messages over the course between two people using it to chat.
That battery unit didn't even drop to the 33% mark, while the devices were always topped off and under heavy use.
Coulda probably gotten away with the smaller one:
But now that I've got a phone, InReach, and Petzl Tikka RXP that all charge from the same micro USB connection, I'll probably keep the bigger Jackery around. (And I did acquire some of the new Eneloop Pro batteries for the Garmin so that's back in service as well.)
Up until that trip I would've laughed and mocked anyone using a cell phone for backcountry navigation, but I'll be damned if it didn't save our bacon. (I trust it a bit more than most phones given the obscene storage capacity, efficient battery use, and the fact that it's waterproof even before adding a case. Sure wish Samsung hadn't butchered the new S6 lineup.)