The other week I went on a 1.5 hour hike with a fully charged battery and GPS tracked the whole thing with MyTracks and I came away with 30-40% of my battery left! Thankfully for the following week, I remembered to change my phone into airplane mode for the same hike and it still had 80% charge when I was done.
Here’s how to do it for all the noobs – hold the power button down for about one second, and you will be prompted with the menu to the right here. Touch the “Airplane Mode” option. To turn it off again, simply do the same thing.