Mophie Juice Pack Air
www.mophie.com/mophie-juice-pack-air-iPhone-4-4S-battery-case-p/1145_jpa-ip4-blk.htm
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
Get on-the-go power for the iPhone 4 & 4S! The juice pack air for iPhone is a rechargeable external battery all in a protective and stylish award-winning design that even enhances sound! Compatible with all iPhone 4 & 4S models.