You know the drill. Your smartphone's battery rarely lasts a full day, but carrying around a clunky external backup sounds like a hassle coupled with a burden. Unless you've opted for Vorson's Bookmark which packs a 2,500 mAh battery into a remarkably thin housing that's just 4.7 millimeters thick. There are magazines thicker than that, so this should easily disappear inside your bag.

On its bulging bottom you'll find a standard-sized USB port, as well as touch-to-activate battery meter so you always know how much juice is left. The $60 Bookmark even offers enough current to charge larger devices like the iPad Air, which it actually manages to out-thin by 2.8 millimeters. [Vorson]