WOW! A knee-powered charging unit. What next? Flatulence-powered stoves?

Geeze Oh MAN (as Radar O'Rielly used to say) I never expected this much response to such a geeky question. Thanks everyone.

I've decided that, even though I do backpack in the southwest, I'll just carry extra Lithium batteries. The state of solar panels tech right now is not where it seems practical for backpacking. Maybe in a few years a 25 watt panel will be as small as a present day 5 watt panel and much more efficient in overcast conditions.

Eric
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"There are no comfortable backpacks. Some are just less uncomfortable than others."