Nelson Technologies has introduced the US$79.95 SaFPWR battery case (http://www.iphonecasewithbattery.com/iphone-4-fusion), dubbed the Fusion, for the iPhone 4. The thin case sports a rechargeable battery case that purportedly more than doubles the time of your Apple smartphone.

The rechargeable iPhone 4 battery case is designed to protect the iPhone from ordinary wear and tear with a low profile design that allows you to keep the original look and feel of your iPhone 4. The SaFPWR technology promises up to 42 extra hours of audio, 11 extra hours of video play back and over two more days of total runtime.

SaFPWR batteries also protect smart phones from short-circuiting, overcharging, and over-discharging by harnessing a proprietary, built-in technology, according to the folks at Nelson Technologies.

The Fusion case adds less than ¬†of an inch in total width or depth to your iPhone 4 and weighs less than 2.4 ounces. You can access all your iPhone 4 functions while it’s in the battery case. What’s more, you can charge Fusion and your iPhone simultaneously through the included micro USB cable. You can also sync your iPhone to iTunes while it’s in the case with the included cable.

Four LEDs on the back of the case let you know on how much power is left in the SaFPWR Battery. The LEDs also keep you updated on your phone’s charging status when it’s plugged in.