At just 0.22 inches thin, the LithiumCard Wallet Battery easily fits in your pocket, meaning you have 1200mAh of backup power at all times. You can currently grab one for $20 shipped via TechnoBuffalo Deals, with Lightning and micro-USB versions available.
With a shell made from aluminum, the LithiumCard is sleek and durable. As the name suggests, this battery is designed to fit comfortably inside your wallet. Alternatively, you could use the supplied NanoStik pad to attach the battery to the inside of your bag, for instance. Despite only measuring 3.37 inches on its longest side, the battery has a pair of flip-out cables for the simultaneous charging of two devices. At top speed, the LithiumCard can replenish 1% of battery power on your device for every minute of charging.
The current deal wipes 66% off the usual price for the LithiumCard, with free shipping to anywhere in the Continental US. Along with a choice of connectors, you can choose between black and silver finishes.