AH! Go green? Use a solar cell, stand in the sun, and augment this source with a beanie cap replete with generator on the wee blade.
That’s nice. Solar and wind power. Note, get back in that brighter light, and keep running in circles. Your wind beanie will slow down.
Actually, the Energizer gizmo uses a DC/DC converter (charge pump) like automotive power amplifiers do, bringing the 3v supplied by two AA batteries up to 5v. See the problem? Efficiency rears its head again. That’s why they recommend using the Lithium e2 batteries, at over $5 a pair.
Don’t get me wrong, the tradeoff in size and convenience is great.
There is another inexpensive option, available (I’m sure it is) via Internet or your local Radio Hut Shack. Explain this idea slowly, before you’re sold a new cell phone instead: they have a USB battery unit that charges from your PC or a USB wall outlet, with a handy port on the side for charging your Sansa (or any USB portable device). If I recall, it’s only $20.
The Clip, when the battery is low, will draw just under 200mA for the initial charge, then it tapers off. Most charge schemes for lithium batteries work in this mode. I’d bet that the slightly larger rechargeable battery unit will work out better for you, especially on an extended trip. It should handle a few Clip recharges.