Nelson Technologies, LLC reaches agreement with SigFx the manufacturer of SaFPWR products. SaFPWR technology has been harnessed into iPhone Battery Cases and increase the runtime of your iPhone for up to two days. The SaFPWR products are by far the best iPhone case with battery on the market. SaFPWR iPhone 4 battery cases have passed the strict performance tests by an Apple designated test lab. Not only are they sleek and modern but their technology trumps any iPhone accessory out there today.