Groupon offers the refurbished Mophie Juice Pack Air 1,700mAh Charging Case for iPhone 4 / 4s in Red for $19.99 with free shipping. That's $5 below last week's mention and the lowest price we could find by $40 for a new unit. This 1,700mAh battery pack provides up to 10 hours of talk time or up to eight hours on the Internet.

A 90-day Mophie warranty applies.