There are hundreds of external battery packs out there, and most of them are highly similar to one another: cosmetics aside, their capacities, features, and pricing tend to be predictable. Anker’s 2nd Gen Astro E7 ($80) is a complete outlier. It has the highest capacity of any external battery pack I’ve ever tested, yet it’s priced competitively with products that deliver half as much juice.

If you have an iPad or plan to carry your iPhone around without access to wall power, Astro E7 is as close to a must-have battery as I’ve seen. Delivered in efficiently designed, eco-friendly packaging, it quickly earned a place in my personal travel bag, for reasons I’ll explain below.

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