iPhone 6 battery (L) and Intelligent Energy UPP fuel cell-based recharger. A fuel-cell fits inside the iPhone. (Credit: iFixit, Intelligent Energy) Intelligent Energy, primarily an intellectual property firm (based in the U.K.), has developed a prototype of an iPhone 6 that runs for a week on one charge. The phone — which hasn’t been modified cosmetically except for tiny vents – uses both a rechargeable battery and a hydrogen fuel cell. The news was first…