I bought a Mophie Juice Pack for my iPhone 4 as I needed a new bumper or case for the phone because of the reception issue and it's great. For those that are unfamiliar, it's a case for iPhone 4 or 4s but it's also a back-up battery. It's obviously bulkier than a bumper but I prefer the way it fits in my hand...way more comfortable and it doubles the battery life so I never worry when I leave the house about running out of charge. You can set it to drain first then use the iPhone battery or iPhone first until it's low and switch to the juice pack. It cost $99 for the plus less for the regular one. Has anyone else tried one? Are there similar products out there like this? Love to hear feedback. It also has LED lights on the bottom to let you know the packs charge...nice and you can charge your phone and pack without taking the phone out of the Mophie.