Keep these things in mind. Phones do not relay off satellites. They relay off transfer towers and I don't think the towers are actually tracking satellites either so there is just too much garbage to go through for GPS tracking with a phone. I use a Garmin GPSMap60CSx. Other than checking biological functions, you wouldn't believe everything you can track with a true mapping GPS and my batteries last 25 hours.
It was said earlier that GPSs are not accurate. Fact is, they are insanely accurate within about 15 feet or so. The biggest mistake most people make when tracking bicycle or hiking tracks is that they do not reset their GPS to zero AFTER the GPS has fully acquired all satellites. If you start a GPS and just take off, it is liable to make its first reading in the place it was turned off last. I've had tracks where the first way point and the second one are 645 miles apart and only took 4 seconds to close that gap. To fix this, wait until satellites are fully acquired then zero out your GPS. Another way is to check recorded tracks after your ride and look to see if there are anomalies in the first track point or two and simply delete them if they are.
The greatest use for a GPS on a bike is the triangulated altimeter and a barometric altimeter. Then there is total ascent then moving average, overall average, max speed, time sitting still and the list goes on. At the end of the day I get to spill my ride track out on to either a road or a topo map. The uses for a GPS are endless.
Then I get to show you fun stuff like this:
