Bushnell SolarWrap 250 Battery

Sun-powered battery

The solar panel paradox: More surface area equals more juice, but also takes up more pack space. That’s why we love this sub-shaped rollable model, made with a flexible film rather than rigid panels. The light-yet-rugged case holds an ultra-thin, 17-inch solar panel wrapped around an enclosed 5-mAh* rechargeable lithium ion battery.

Colorado testers recharged the power pack in six to seven hours under direct sunlight (faster than most similarly sized units we’ve tried), which then was able to refill an 80-percent depleted smartphone in less than an hour. Caveat: While this unit charges USB devices faster than others we’ve tested, it takes a while to fill (even from a wall it takes four hours). $155; 9.2 oz.; bushnell.com

*mAh Milliampere-hour: a unit of electrical charge; higher number means more juice.