Do a search on the Internet on how to optimize your particular phone to increase battery life. It's a simple matter of changing some settings to some of the apps that you have on your phone that really don't require certain phone functions and making sure that there are no apps running in the background other than your cycling app. I did it on my iPhone 5c and I have done centuries, without the need to recharge the phone, and had plenty of battery life left for emergency calls. As of now, my iPhone goes through roughly 10% battery life for each hour I ride with the GPS turned on. If you plan on a long ride and plan on very long stops, you only need to pause your cycling app when you stop so it doesn't use the GPS. You just need to remember to start the ride back up after your break. An advantage that you have with using a phone for your cycling computer is that it's much cheaper to try different cycling apps until you find the one you want than it is to try different GPS cycling computers. If you want to be able to see your speed, miles and other data without having to turn on your phone's screen, look at the Wahoo RFLKT and RFLKT+ devices. Not all cycling apps work with this device but the most popular ones do. Wahoo does have it's own cycling app called Wahoo Fitness that's free, but it leaves a lot to be desired.