The basic case design is quite similar between offGRID and NuCharge. Both are black plastic sleds, offGRID glossy- and NuCharge matte-finished, designed to be as small as can be by battery case standards—they’re noticeably shorter and thinner than most of their rivals. Your iPhone 4 slides in between two plastic side walls and a Dock Connector plug fits into the port on the bottom of the device. All of the back, except for the camera and…