Originally Posted by
hagak
I use cyclemeter elite and with an iiphone 6s have found the elevation to be pretty spot on, course I am using the barometer. I also find the speed/distance to be accurate as well but I am using a wahoo speed/cadence sensor. That said I have outgrown it since I am biking further distances I have to carry an external battery to just barely have enough battery time. So will be picking up a Wahoo Elemnt to replace it.
You may also want to look at the Wahoo RFLKT as well. While not as fancy or as expensive ($79 USD) as the Elemnt, it will display almost any data value that Cyclemeter tracks and the screen is so user defined that you can place that data anywhere you want it. I use one, along with HRM and speed/cadence sensors, and can ride well over 4 hours and still have about 50% of my phone's battery life left after the ride. And I'm using an iPhone 5c that's over two years old with the original battery.
Here's a
web site with some tips to help extend the battery life of an iPhone. It has some stuff for an iPhone 7 but if it doesn't apply to your iPhone, like a new feature, you can skip over it.