How much money do you want to spend? All of the portable chargers reviewed here cost $70 or less. Most range between $20 and $30, but those can charge only one device at a time.
How many devices will you charge at once? If you need to charge only one device at a time, there are plenty of quality, affordable options. If you're a power user who needs to charge several devices on the road, go for a high-capacity charger.
Does your phone/tablet support Quick Charge technology? With a compatible charger, such as the Aukey PB-T1 (Est. $30), Quick Charge powers up a device's battery up to 75 percent faster.
How much power will you need? Most portable chargers store enough power to charge a typical cell phone or similar low-demand device once or twice. Power-guzzlers like iPads demand too much juice for some lower-capacity portable chargers; look for portable chargers with capacities of 10,000 mAh and up for tablet charging to their full capacity.
Do you want a charger you can carry in your pocket? You can carry pretty much any portable charger comfortably in a briefcase, backpack, etc. -- even high-capacity chargers that will last through a week-long camping trip weigh just about a pound. But if you want something you can carry in your pocket every day, opt for a regular or mini charger that can just charge a smartphone once or twice.
What else do you need? Portable chargers come pretty devoid of extras in the box. For example, fastest recharge times require using a wall-outlet charger, but you'll rarely find one included (instead, you can use the charger that came with you mobile device). Ditto for connecting cables outside of a standard micro USB to USB cable that serves to connect the external battery pack to either a charging source or your mobile device, depending on whether it is charging or being charged. You'll need to budget extra for anything else, including, in many cases, cables to connect to Apple devices.
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 portable chargers are more efficient than others. Most deliver efficiencies in the 70 to 80 percent range, meaning a 10,000 mAh device will deliver about 7,000 to 8,000 mAh. External factors -- notably the quality of the connecting cable -- can effect efficiency as well. To ensure maximum efficiency, use the cables recommended by the charger's manufacturer
Green energy solutions can be a good thing, and portable chargers are no exception. Up-and-coming within this category are solar chargers. Although plenty of good solar chargers are on the market, they have a ways to go before they can compete with grid-powered devices. Their primary drawbacks are long charging times and cloudy days. Other charging solutions include those powered by salt water and hand cranks. Like solar chargers, performance and value make them an iffy solution -- for now.