Here are some of the examples I refer to in paragraph 3. This one accepts 6 AAA batteries:
This one accepts either 2 or 4 AAA batteries:
This one accepts 4 AA batteries:
Sure, these chargers would add some weight, but consider that the Garmin 400t weights 7.5oz with batteries, whereas the current generation iPhone weighs 4.8oz, and you might end up with a lighter system. I would also argue that a AA or AAA charger would be better than a replaceable proprietary battery for thru-hikers.
I won't compare lighter Garmin GPSs because they don't offer the topo mapping feature of the 400t. Am I correct that the 400t cannot import national Geographic 24K maps like the Magellan Triton? GPS cellphones have had 24K scanned maps for years now.
Anyway, so the extended battery problem can be solved at a lighter weight (assuming iPhone v2 weighs the same and these chargers are no more than 2.7 oz). The real question, then, would be which device is more efficient. We'd have to turn off the iPhone radios and run some tests. Even if the iPhone were less efficient, if it replaces other devices you'd be carrying (mp3 player, cellphone), you'd still be lighter.
Oh, and don't forget the current gen. iPhone is $130-$230 cheaper than the Garmin, and the iPhone's screen has approx. twice the resolution.
So back on the main subject, I guess I just get a little worked up when I see Garmin touting these bulky, expensive, proprietary devices with very poor mapping ability and non-intuitive UI, when for years GPS phones have been able to do better. GPS phones were 2 years ahead of Garmin with high sensitivity receivers, 5 years ahead of the 24K topo maps, and are still ahead with the high resolution screens. You can complain that GPS phones aren't as rugged, but then neither is your cuben shelter. I say if you have to have a rugged GPS with long battery life, stick with a Garmin Geko 301. But if you want all the frills of digital color 24K topo maps, don't go spending $630 (the price of a decent laptop these days) on a uni-tasker that will be outdated as fast as a cellphone, when several cellphones have for years been doing better than even Garmin's latest model.