I have seen some pretty small mobile phone battery chargers before, and the smallest has been the one by Devotec which is a little larger than a quarter. I believe the Devotec one is a Kickstarter project, but the Tarot is available now.
The Tarot, which I can only assume is named after the cards, is about the size of a credit card. It is somewhat thick at 0.28, which is not as thin as the Chargecard. However, the Chargecard was not intended to be a battery, but a charging cord.
The weight is 1.79 oz, and it has a 1,500 mAh capacity. It also has a USB adapter so you can charge it quick, and the customary LED lights to show how much power it has.
You should be able to get it on the Powerock USA website for about $34.99.