BuyDig through eBay has the uNu Enerpak 5,000mAh USB Battery Pack for $29 (59.95 – 30.95 instant savings) with Free Shipping for limited time. Deal expires January 6, 2013, 10:59 am ETS.

This portable battery back is compatible with iPhone 4/4S/5, Android Phones, Blackberrys, and most USB devices. It is able to re-charge almost any smartphone up to 2.5x while still managing to remain light-weight and completely portable.