I don't know about the GPS thing. My cell phone has one in it and the damn thing is tiny!
Yes, but the cell phone itself is not that small. The GPS chip in your phone uses the prexisting battery and antenna.
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To steer back to topic....
How may nature breaks do the pros require during a 5 hour stage? I've yet to requre one during a 3-hour ride, and my weight indicates that I'm not H2O deprived--is it a case of drinking too much fluid?