Though it’s not owned by Apple, Incase has repeatedly riffed so successfully on the Cupertino-based company’s designs that its cases, batteries, and chargers have become fixtures in Apple Stores and reference pieces for smaller developers — some have been truly noteworthy and inspired. Most recently, Incase has embraced an almost extreme minimalism in iPhone accessory design, scaling back its earlier approaches by determining the bare minimum required to achieve similar or more modest goals with fewer materials or components; the most recent result is its Snap Battery Case for iPhone 4 ($60), a deliberate reduction of the spare power cell-slash-protective shell down to its simplest possible implementation.

Rather than leapfrogging or rivaling a growing group of iPhone battery case competitors, the Snap Battery Case covers and powers the iPhone 4 less; it’s designed to let you quickly snap the iPhone 4 in, and go. There’s a 900mAh battery inside a thin back shell, a modestly flexible top plastic frame that leaves only the headphone port and Sleep/Wake Button exposed, and a bottom Dock Connector housing with holes that properly vent the iPhone 4’s bottom speaker and microphone without creating echoes. In a now rare sign of the company’s unique relationship with Apple, the bottom of the case uses a female version of Apple’s Dock Connector—effectively prohibited for use by other third-party developers—to provide pass-through charging features for the device inside. Incase includes a USB to Dock Connector cable that matches the soft touch rubber finish of the Snap Battery Case, too.
And that’s pretty much it.
Except, of course, for the specifics. The female Dock Connector is a significant novelty on cases of this sort, conceivably allowing the iPhone 4 inside to continue working with docks and accessories that the typical battery cases close off by requiring unmitigated access to the iPhone’s identical port. Unfortunately, Incase has turned the Dock Connector around on the case so that you can’t just plug an iPhone 4 into the case and drop it into, say, a speaker system with full access to its screen. Instead, the encased iPhone winds up inserted backwards, such that all you see are the Snap Battery Case’s large power indicator button and otherwise invisible five white power indicator lights, showing the current level of charge. Try to connect an accessory, even a cable, for anything other than supplying power and you’ll find that it doesn’t work. This appears to be a message to developers from Apple: if a pass-through Dock Connector is used on an accessory, it can’t be used in a manner that encourages connection of additional non-cable accessories, even for synchronization.
By choosing to use a 900mAh battery inside the Snap Battery Case, Incase enabled the enclosure to be noticeably thinner than rivals—the overall thickness is comparable to an iPhone 3G or 3GS, versus bulkier competitors that are closer to original iPods in size—but it has also limited the added power. While the company estimates that iPhone 4 talk time can be extended by “up to 3 hours,” or 3/7 of a full recharge, our test of the battery showed only a 34% actual increase in battery life as the iPhone 4 jumped from 5% to 39% when it wasn’t being used for anything else. This is a little better than a third the power of Juice Pack Plus at 3/5 the price, with less protection.
On that note, what Incase has done with Snap Battery Case’s frame is interesting. As with some of its earlier Snap Cases, the iPhone is recessed by a millimeter or so relative to the case’s plastic face, so laying the screen upside down on a flat surface won’t cause scratches. But there’s no other screen protection, button protection, or side protection here; Incase has covered just enough of the iPhone 4’s sides to prevent antenna bridging with the infamous iPhone 4 “death grip,” but no more. As battery cases go, this one’s as simple as they get.