As one of its daily deals, All4Cellular offers the refurbished Mophie Juice Pack Air for iPhone 4 and 4S in Black/Silver (pictured) or White, model no. 1146_JPAXP4, for $19.99 with free shipping. That's $10 under our mention of a refurb from three weeks ago and $32 under the lowest total price we could find for a new unit today. This 1,500mAh battery pack provides up to an extra 6 hours of talk time in 3G or up to 12 hours in 2G. Deal ends today.

Note: A 90-day All4Cellular warranty applies.