Every personal electronic device needs power. Power cords snake across airport lobbies and trip people up at home, and power supplies and AC/DC adapters are nuisances to carry. Frequent travelers know that the search for power can become desperate at times. Portable devices like smartphones, tablets, iPods and small laptops are equipped with built-in rechargeable batteries that always seem to need recharging at the worst moment.
Portable chargers -- also called external battery packs, power packs and external power supplies -- eliminate the need to find an outlet while you're on the go; just grab a USB cord and let your device charge. The most powerful portable chargers typically cost from $50 to $100, but models tailored for smartphones and MP3 players are also available for $30 or less. Beyond cost, the amount of power portable chargers store (measured in milliamps per hour, or mAh), and their power and speed (indicated by volts and amps) are both important.
Numbers don't tell the whole story, however. A 3,000 mAh battery, for example, might not provide as much juice as a 2,800 mAh because the batteries themselves are sucking up power while charging devices and some products are more efficient than others. Most are around the 70 to 80 percent range, meaning a 10,000 mAh device will give you about 7,000 to 8,000 mAh. To ensure maximum efficiency, use the USB cables recommended by the charger's manufacturer. (Newer-model Apple devices require lightning cables instead of 30-pin connectors.)
Portable chargers are lighter, smaller and more ruggedly designed than ever before, making them more convenient and mobile. External power supplies the size of a keychain or lipstick tube (the trend of the moment for smaller chargers) can power up a smartphone twice over. On the other end of the spectrum, powerful chargers with up to 20,000 amps that can juice up to three devices at once -- or even a small laptop -- are about the size of a smartphone and weigh just about a pound. Both take anywhere between a few hours to overnight to recharge, depending on their size, but bigger, higher-capacity portable chargers can power up devices faster than their mini counterparts. That's another important consideration -- the charger itself also needs to be charged.
The high capacity of portable chargers -- particularly given their pocketable size -- was unheard of just two years ago. External battery chargers are a fast-growing and dynamic market, with newbies like Kickstarter success story Limeade competing with industry leaders like Anker, Jackery and New Trent. There are hundreds of portable USB chargers to choose from, and it's generally advised to get one that comes with a warranty, given that some counterfeit products and lemons have hit the market. (Most manufacturers say their portable chargers are good for 500 or more full charges.) Most reputable portable chargers also have protection against overcharging, so they won't damage or overheat your devices.
Perhaps because there are so many portable chargers on the market, there aren't as many professional reviews from highly reputable tech sites as one would expect. Many bloggers and travel- or Apple-focused sites do offer valuable insight and critical reviews, however. After poring over test reviews and hundreds of customer reviews, we've found the best portable chargers based on design and performance.