For an iPhone, the best cycling app out there is Cyclemeter. If you must have turn-by-turn, stay with RideWithGPS. The folks at Cyclemeter are working on it but put it off for full support of the Apple Watch. If you want to conserve your battery life on your phone there are several things that you can do so that your battery will last for your entire ride, regardless of what the diehard Garmin users tell you. Do an internet search on ways to extend your battery life. I use an iPhone 5c that's about 2 1/2 years old. I went through each app and turned off notifications for any app that I don't care to receive notifications from. There are also some system settings that you can change that will keep the phone from using up battery power. Also, before you start your ride, swipe off all apps running in the background except your cycling app. That keeps all those apps from using up any cellular or wifi service that they may normally use. Also turn off wifi before your ride. Your cycling app does not need it. If you want to see what your speed, distance, cadence and other data during your ride, you may want to look at the Wahoo RFLKT which will connect to your phone and display whatever data your compatible cycling app sends it. RWGPS is compatible with the RFLKT, which is only $79.00. If you have Ant+ sensors that you used with your Garmins, the RFLKT+ will bridge the Ant+ signals and convert them to Bluetooth LE.

I use the RFLKT+ on my iPhone along with Wahoo's TICKR HRM and their Blue SC speed/cadence sensor. Doing the above, my 2 1/2 year old battery drains about 10% per hour. When my phone was new, I did a century without having to recharge my battery and still had enough battery life left to make an emergency call, if needed. Since the battery is much older now, I carry a USB charger on any ride over 65 miles, just in case. I did a 56 mile ride yesterday and didn't need it.