GPS on any platform
"Intensive use of GPS depletes a battery rapidly on any platform."
This is really just a phone problem: based on experience with my ancient Mk1 Garmin etrex, I suspect that much of the power drain is due to downloading maps, LED colour displays and having to run a JVM-based system. Users of modern etrex models report up to 43 hours continuous use when power-saving is employed. Runs on a couple of easily replaceable AA batteries; carrying a few pairs of spares isn't much of an issue.
GPS on the phone does have it's place though - in the city. Pure GPS is poor in cities because the buildings block much of the sky, and especially, the horizons, which give you better accuracy (if you can only see a few GPS sats more or less directly above you, you won't get very good triangulation). Here though, the phone can use cell localisation techniques.