Cases for the iPhone 5 are arriving, but battery-augmented cases for the new iPhone are still largely missing. Since Apple changed to the Lightning connector, every previous battery case won't work with Apple's latest phone.
That leaves many people feeling a bit naked, because the battery life of the iPhone 5 is down a bit from the iPhone 4, and about on par with the iPhone 4S. The delay is the Lightning connector. It's proprietary to Apple, and while Apple will license and approve products, it's not happening at "lightning" speed.
For heavy users, the built-in battery of the iPhone 5 likely won't make it through an entire day. I checked around to see what's happening with production of new battery cases, and I wouldn't expect anything soon.
Mophie, who makes popular battery cases for previous iPhones won't commit to a date, but you can sign up to be emailed with availability information.
Lenmar has announced a new battery case, and priced it at US$69.99, but it has a release date of December 24, 2012. Boostcase says it has an iPhone 5 battery case coming, but offered no details and no date.
Some people who can't wait are going for external booster batteries, but they are a bit of a pain. As far as saving your internal battery goes, some people claim turning off LTE reception when you are not in an LTE area can really help. You'll find the switch on your iPhone 5 by tapping Settings>General>Cellular and then turning off "Enable LTE."
We'd be interested in your thoughts and solutions, so feel free to let yourself be heard in comments.