iPhone Battery Life

You'd actually be surprised. With no other apps actively running in the background you can expect a device starting with a full charge to last up to 14 hours.
Just lock your phone, put it in your pocket, and shred hard all day.

Tips for great all-day battery life

  • Doing anything on the internet when you have mediocre reception hurts battery life surprisingly more than GPS. You don't have to avoid the internet, but keep in mind streaming music or constantly checking Facebook on lifts is going to hurt battery life.
  • Keep your phone warm(-ish) as a cold phone gets worse battery life.
  • Lock your phone (hit the power button) after you start recording. Slopes will go into the background and save power by not having to constantly update the info on-screen.
  • You can turn off cellular data (Settings app -> Cellular) for the biggest battery savings. Don't use Airplane mode, as it will degrade GPS accuracy.

My Testing

I'm always testing battery consumption and aim for reasonably real-world metrics.
During most recent tests using an iPhone 5, the app used an average of 7% battery life per hour. During these tests I quit background-fetching apps like Facebook before hitting the mountain, but left wifi/cell/bluetooth on.