You could also buy a battery pack, and track constantly with Gaia GPS.
I have this $30 one from Amazon... it claims it will charge your iPhone 9.3 times, and I don't doubt it, though I've never had the need: http://www.amazon.com/AmazonBasics-Portable-Power-Bank-100/dp/B00ZQ4JQAA/ref=zg_bs_7073960011_12
I use this battery pack for multi-day backpacking trips, and travel in general.
p.s. I'm one the Gaia GPS founders/developers.