NetDirectBargains via eBay offers the Mophie JuicePack Reserve Battery Pack for iPhone and iPod in Black/Silver, model no. 1135_JPU-Reserve, for $15.49. With free shipping, it's the lowest total price we could find by $4, although we saw it for $5 less last fall as part of a Facebook promotion. This 1000mAh battery pack purports to charge your device twice as fast as conventional batteries. It features a retractable 30-Pin connector, built-in carabiner keychain, and micro USB cable.

Of note, the product page states compatibility with Apple iPad; however, we cannot find anything to support this claim on Mophie's site.