no doubt you've already acquired a GPS by now. you did not mention what type phone you use? iPhone 4 here. I use it to track (map) and capture speed/cadence/distance from Garmin SC10 unit. I have been commuting and doing charity rides with it. since a couple generations of hardware and iOS updates back I have never run out of battery. My last metric century was a lot of fun. When it was done I was amazed how much battery I had left more than 75% battery by the way. Granted the new iPhone 4S is a new animal and yes it has a battery problem which appears to be a software fault and related to time zone issues? Surely they will resolve that sooner than later as they have previously with other issues. If you are doing longer rides than centuries get an external battery pack for it if you really think it won't make it that far. Other smartphones will work as well. I like using the iPhone as it's one less thing I have to carry or attach to the bike. If I have any problem the phone is right there. now all I need to do is figure out how to use the iPhone to make me go faster...