NetDirectBargains via eBay offers the Mophie JuicePack Reserve Battery Pack for iPhone and iPod in Black/Silver for $18.99. (DirectDeals4U via Amazon charges the same price.) With free shipping, it's the lowest total price we could find by $21, although we saw it for $4 less three weeks ago (since expired). This 1,000mAh 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.