Just returned from extensive walking and navigating in a large city. I found that the latest and greatest Garmin had trouble acquiring and maintaining a signal in the urban canyons and that the iphone actually navigated better and more consistently. I bought a Mophie battery extender for my iphone as I was going through the battery so quickly. The advantage of this is that you do not have to turn off your phone or wait for it to charge up. You can use it in conjunction with your iphone battery. I did not get quite double the normal battery life of the iphone, but it was about 1 and 3/4 the normal life. It generally carried me through a full day, and I used the Garmin for those times outside the urban canyons.