Bringing iphone on a 10 hour trail

Hi,
I'm doing a 50 km trail run in 2 weeks. It is a 25km unmarked trail and most participants know the route. I have done 1 loop but looking to use an iphone 6 app called view ranger to check on my progress from time to time. Not sure if the battery will hold up, I will be checking/opening the app from time to time. Anyone have experience with navigating with an iphone over a long day, anyone tried a backup battery pack such as http://www.lifeproof.com/en/fre-power-case-for-iphone-6/

Thanks,
Uinsean

I haven't used battery-case combinations like the link you provided, but I have used cheap USB chargers like this: http://www.amazon.com/Duracell-Instant-Charger-Includes-Universal/dp/B002FU6KF2 ... it's just like plugging into the wall or your computer so you can still use the phone while it is charging. I can't say exactly, but one of those USB chargers would probably charge your phone up once.

Another tip is to put your phone in Airplane mode. The battery will last a LONG time that way. When you want to check your progress, take it out of airplane mode and let it sync. I'm assuming the re-sync/connect progress would be quick.