Anker's Astro Pro2 is a monster of an external battery, offering 20,000 mAh and multiple ports. It can charge just about anything -- from a camcorder to a phone to a netbook -- and comes with a slew of connectors and cables. At $80, the Astro Pro2 is on the low end, price-wise, for such a powerful portable charger.
A book-sized mega-charger. The Anker Astro Pro2 is a thoroughbred among portable USB chargers, delivering 20,000 mAh and boasting an impressive four ports. It has a maximum output of 4.5 amps among its four ports and can even power up small electronics (like a lower-powered laptop or camcorder) through an output that can be switched to 9V or 12V. The Astro Pro2 comes in basic black and is about the size of a large smartphone; it's definitely on the bigger side for a portable USB charger, weighing just over a pound, but is also slim. The LCD screen displays the power level as an exact percentage, which reviewers prefer over light indicators, which are harder to read. The screen also shows the charging status and voltage selection.
Built to charge an iPhone 10 times over. Anker claims the Astro Pro2 can charge an iPhone 10 times, a Galaxy S4 six times and tablets multiple times. It's ideal for those who need a lot of juice, like multiple device users who find themselves off the grid for a while. With its 9V or 12V ports, the Astro Pro2 can also power up a small laptop. Most Amazon.com users give the Astro Pro2 rave reviews for powering up multiple devices quickly, and for a fast recharge, though there are some minor complaints. In one professional test the Astro Pro2 had 80 percent efficiency -- the high end for portable chargers. It's as fast as a wall charger with just one device, but even with three devices it speeds along, AndroidPolice.com editors report. The Astro Pro2 comes with a 110-240V AC adapter that Anker says recharges the battery in about five hours.
Over 250 Amazon.com contributors give the Anker Astro Pro2 4.5 out of 5 stars, praising its speedy charge and solid design. A handful of reviewers report the product did not work.
Review: Anker Astro Pro2, Contributors to Amazon.com, As of April 2014
2. EnigmaTech News
The U.K.'s EnigmaTech News is one of the few sites to test the Astro Pro2 20,000 mAh; it charges a Nexus 4 from 10 percent to full four times. Ollie Ford calls the Pro2 "a solid device" and "far superior to any other external battery I've seen."
Review: Anker Astro Pro2 20,000mAh, Ollie Ford, Aug. 31, 2013
This Astro Pro2 test review finds the charger functions at about 80 percent efficiency, which is at the higher end for portable USB chargers. (Voltage conversions and other issues cause the battery to lose power while it's operating.) Ryan Whitwam calls it "a battery for a serious traveler, or for someone with three or four devices, some of which need DC input."
Review: Anker 2nd Gen Astro Pro2, Ryan Whitwam, Feb. 10, 2014
4. International Business Times
The Anker Astro Pro2 Multi-Voltage is among 10 portable battery chargers listed (but not tested) in this article. The Astro 2 is praised for providing enough power to charge numerous devices or a laptop.
Review: 10 Best Battery Life Extenders, Ryan Inoyori, Oct. 7, 2013
HuffingtonPost.com lists the Astro Pro2 as one of several external battery chargers, noting its 20,000 mAh and aluminum exterior. Although Jonathan Handel tests each charger with the S4, he only gives short write-ups for each.
Review: Power Banks (External Batteries) Review, Jonathan Handel, July 28, 2013