I'm going to be going into rural Nepal for 8 months starting this winter. I would like to be able to take pictures for this time. However, there will be no electricity. I've got a nikon coolpix 4500, which uses a Li-ion rechargeable battery (#EN-EL1) which is 7.4V / 680mA. The proprietary charger (#MH-53) takes AC at 100-240V and outputs DC 8.4V / 600mA. The MH-53 supplies only a slightly greater power than the EN-EL1 (5.04W vs. 5.032W) Anyway, I'd like to design a design a charger that acts as a substitute for the EN-EL1. I plan on doing this with a solar panel, which will probably end up being 7-10W, outputting, ideally at the .6A that the charger would. However, I suspect that the panel will end up being quite a variable source, and, as I don't want to damage the battery, I'll need to stabilize it to outputting at 8.4V/.6A. Now, I've never done this sort of thing before, but I've taken an E&M class recently and would be confidant putting anything that's relatively simple together. Having done some research already I think that if the panel put off a constant flow at .6A, then I could use something like the LM338 in conjunction with a few resistors (and perhaps a potentiometer, in case I'd like to re-use the system for something else) to regulate the voltage to the 8.4V. However, this will probably not be the case. http://www.national.com/ds/LM/LM138.pdf details a 'adjustable current regulator' (on page 12) that looks to be something, but I don't know. (help?) Ultimately, is there a self-contained object that I can build that, having a variable source put into it, outputs a pre-set current at a pre-set voltage? Or is there no way to get around not having a constant current to start with? Thanks for your help.