We came across this neat little MicroUSB / Apple Lightning battery pack made by Cherry that is slim enough to fit in your wallet. Coming in at a thickness of 4.8 mm the Cherry Power Card is not much bigger than a credit card and will discreetly fit into your wallet and be ready should you run low on battery juice. The 1500 mAh battery will charge most smartphones these days up to 50%. Available in Metallic Silver, Caribbean Blue, Premium Gold, and even Hot Pink to match your style, and go for $34.99 each.

Cherry Power Card - $ 34.99