the beat charger i have found foe the iphone is a product called proporta turbo charger, it gives you 5 full charges, and does them very quickly, has really helped when i'm out for 3 or 4 days.
I've been using viewranger myself for a bit too and quite like it, some good features and new ones all the time with updates. you can record tracks, convert them to routes and export them for viewing on a pc, routes can also be uploaded, by just copying them to your viewranger folder on the sd card. Another feature which i sure i read that the mounting rescue are using is the "buddy beacon", basically it transmits your location to another viewranger device or a secure webpage, maybe handy if you get in trouble or are late returing. locus is also good and free with adds (android) lots of differant maps to choose from including os maps, a network siganl is required to update maps, it's suposed to be possible to download sections of the maps to your sd card, but i have never been able to view them off line after doing this, it can be used for geocaching too.