If Apple's iPad Air 3 indeed comes with a 4K display, it will surpass the premium iPad Pro in terms of screen resolution. However, 9to5Mac says that this is unlikely as the iPad Pro is the premium one and is supposed to feature specifications much better than iPad Air devices.
As far as an improved battery life is concerned, the iPad Air 2 already possesses a large battery with a longer life compared to other tablets. it is possible that rather than replacing the existing battery, Apple may introduce new battery saving features to let you optimize your iPad's battery life to a greater extent.
A number of other rumours also point towards iPad Air 3 sporting a rear-facing LED flash as well as additional speakers. The display is said to be 9.7-inch long and you will be able to use the Apple Pencil on it as well.
Apart from the iPad Air 3, Apple is also expected to launch several new models of the Apple Watch which will include several colour options for the Sport and Hermes bands along with a Black Milanese Loop variant. The event will also witness the launch of iOS 9.3 and WatchOS 2.2 operating systems for the new devices.