Who should get this

Honestly, a lot of people looking for a portable power solution are going to be better off starting with a USB battery pack. Our large battery pick will keep a smartphone charged every night for a week and is no bigger than a paperback novel. But if you can't be sure of your power needs, a solar charger could refill a small battery pack in a day or directly charge a smartphone in two to three hours.

The catch is that these chargers work only with USB devices, which limits their appeal for those who need them for long-term, off-grid setups. If that's you, you'll probably be more interested in the larger setups from companies like Goal Zero or Suntactics. In the future, we may review these units, but for now, they're outside the scope of this guide.

How we picked and tested

The Anker (bottom) and the now discontinued runner-up RAVPower (top) both returned to full-speed charging immediately after being shaded. Photo: Mark Smirniotis

We started with a pool of solar battery charger contenders culled from Amazon sales and user reviews, as well as authoritative review sites like OutdoorGearLab. In our survey of more than 400 readers, more than 40 percent said they would want to be able to charge a tablet and 59 percent said they wanted to spend less than $75, so we considered only models that can produce at least 2 amps, and ruled out some more-expensive offerings.

With cloudless, blue Southern California skies and an expected high in the 70s, we set out the panels we chose for testing at roughly a 25-degree angle at 10 a.m. and connected them to a PortaPow V2 Premium USB Power Monitor and an external USB battery. We disqualified any chargers unable to get back to their maximum output on their own once shaded. If you decide to leave your phone and solar charger out all afternoon to absorb some juice while you're off hiking, you'd be pretty disappointed to find your phone charged for only a total of 15 minutes before a cloud passed by. That's a dealbreaker.

Because we had a few models that didn't carry this quirk, we tested them against one another to gauge power production. When they performed similarly, we chose the lighter, more compact of the three competitors as our winner.

Our pick

The PowerPort Solar Lite is the smallest and lightest charger we've tested that's rated at 15 watts. Photo: Mark Smirniotis

If you need power for small devices when you're away from electrical outlets for more than a couple of days, the Anker PowerPort Solar Lite has the best combination of charging speed, size, and price. Used alone, the Anker can fully recharge small tablets or one or two smartphones in one sunny day. If you pair the Anker with one of our favorite USB battery packs, the combination will have enough juice to keep your USB-powered gadgets fully charged every day for as long as needed. And although half of the chargers we tested slowed to a crawl when a cloud passed overhead, the Anker resumed full-speed charging almost immediately after the cloud was gone.

In direct winter sun, our peak measurement was 8.48 watts/1.67 amps, which may seem low compared with the 15 watts/2.1 amps production advertised in the specs. But after an entire day charging our test battery, the average 6 watts/1.17 amps got us 85 percent of the way to the total produced by the much larger and heavier RAVPower charger.

The Anker measures about 18 inches long when fully deployed—about half as long as the 31-inch RAVPower, making it much easier to orient toward the sun. Folded up and ready for travel, it measures 11 by 6.3 inches and weighs just 12.5 ounces. Models any larger don't get you enough performance boost to justify the size, and any smaller won't be able to keep up with modern, power-hungry gadgets. If anything goes wrong, Anker offers solid customer support, an 18-month warranty, and a track record of quality power accessories.

How to get the most from your charger

Making power from starlight. Photo: Mark Smirniotis

To really max out your power output, you'll want your panels angled correctly. A good rule of thumb is that the panel's angle, relative to flat ground, should be roughly the same as your latitude, with some minor adjustments in summer (shallower) or winter (steeper). If you really want to get the most juice, check sites such as solarpaneltilt.com, pveducation.org, or Solar Electricity Handbook to figure out the best angle before you go.

This guide may have been updated by The Wirecutter. To see the current recommendation, please go here.