Best value External Cell Phoner Power Supply ?

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http://androidforums.com – Want one of these for when the cell dies while away on vacation, not near an outlet. External battery pack that recharges. Some are junk, but I don't want to pay $50, either. Got a link? Amazon.com: Anker® Astro Slim2 4500mAh Ultra-Slim Portable Charger External Battery Power Pack for Samsung Galaxy S5, S4, S3, iPhone 5S, 5C, 5, 4S, iPad Air, mini, Note 3, HTC One, One 2 (M8), Motorola Droid, MOTO X, LG Optimus and most other USB-cha Any other candidates, or do I get this one? (General)