Those things get discussed on CPF now and then. They're technically cool but my conclusion is always that they're not worth the weight. For urban or vehicle use a conventional charger makes more sense (powered by AC or 12V). For outdoor use, just how much electrical stuff do you want to power, anyway? Obvious candidates: 1) flashlight, an AAA powered one will run 8+ hours with enough light to walk around by (some of them also have high-powered settings that come in handy; 2) GPS, Garmin Geko again runs around 8 hours(?) on two AAA's; 3) FM radio/music player, Sandisk Sansa M200 series runs 10+ hours on one AAA. If you're a little bit careful the four AAA's total should last many days. A spare set is under 2 ounces. Yes you'll eventually need more and/or a way to charge your existing ones, but you'll also eventually need food, and batteries aren't that hard to come by.