Mophie recently announced the availability of a new design for their highly popular and useful juice pack air battery extender for iPhone 4. The Mophie juice pack air snap case (US$79.95) is available at Apple Stores and other retailers, and while it still offers virtually double the battery capacity of the stock iPhone 4, the new design makes it easier to access all of the switches and ports of the smartphone.
Let's look at how the design has changed. The previous model, which I personally use on my iPhone 4 all the time, splits near the top of the phone. That means that when you wanted access to the Dock connector, you basically needed to take the entire case off. That wasn't difficult to do, but it was inconvenient. The old design also had two openings on the left side of the phone for the ringer mute switch and the volume buttons, as well as a two openings on the top -- one for the power switch and the other for the microphone and headphone jack.
The juice pack air snap is quite different. The bottom of the case snaps off, so you can leave the case on the iPhone if you need access to the Dock connector. The same four LEDs for determining charge status are still there, there's still a micro-USB port on one side for charging the case, and the tiny slide switch for "charging" and "standby" is there as well.