I'm preparing for a 480 mile thru-hike of the Colorado Trail myself next summer and just got done reading Andrew Skurka's book (which I highly recommend, along with his blog). As a result, I'm a complete gram weenie. After doing my research I'm leaning more toward a USB battery like this
if in needed AA batteries, I'd use with one of these usb chargers
Here's my logic. I'm going to be on the move, at least 1/2 of the time in heavy trees or facing the wrong direction for good sunlight to fall on the panel on my back. I'm going to be moving 8-10 hours a day. Most of the solar chargers are marginal at best and will fully charge a cell phone in 8-13 hours of continuous sunlight. They weigh, at the lightest 12 oz. and most are somewhere north of a pound and most cost about $90-130.
One 10000 mah usb charger will hold about 4-5 full charges for my cell phone. It weights 10 oz. It's half the price ($50). I'm going to be stopping in town for food at least every five days, so I can charge it while in town or buy two and ship them home for recharging and get them shipped to me along the trail. I won't have to worry about cloudy days, tree cover, or walking in the wrong direction. There are larger capacity units available as well as smaller, cheaper units (this one just gets exceptionally good reviews).
I know it's not the 100% off the grid solution, but I'm convinced that the off the grid solutions are so marginal for a backpacker that they're not realistic. If I was sitting in camp for eight hours a day I might risk it, but on the trail I just don't think solar is the solution.
Another thing to note is that the Spot needs Lithium batteries to work right and reliably. Given that a set of lithiums will last 14 days with the tracking on, I would just stick to lithiums.
For headlamps, I'm moving away from a dedicated headlamp and toward the Fenix LD 01
flashlight with the reversible clip so it will go on the brim of your hat (warning, there are multiple versions of this light, some put out more light, but are less efficient). It weighs in at 14 grams (without the one AAA battery), which will last up to 27 hours on low (which is adequate to read by), but can also put out 27 lumens (enough to hike by in most terrain) for just over three hours or put out a serious 72 lumens for 90 minutes. That's on one single 11.5 gram AAA battery.
I have a steripen and if I were going with rechargeable batteries, I'd go with the CR123 unit that comes with a solar charging box (and still carry a couple new CR123 lithiums just in case). Since my last hike on the CT last summer I've moved to using a Sawyer SP121 Just Drink water filter
. This is less because I'm a weight weenie and more because I drink from a hydration bladder anyway, so I find it easier and faster to just dip my bladder into any stream, do nothing to treat it, and just drink normally through my tube. While it does occasionally need to be backflushed and stored properly if you aren't using it for an extended period of time, you simply won't find a better warranty than their one million gallon guarantee. No pumping, no chemicals, no batteries, no wasted time and when you get to camp, hang your bladder in a tree and you have a gravity filter.