New 21.5-inch Retina 4K models expected.
MacBook Air Disassembly Photos and Battery Access
MacBook Air Battery
Gizmodo provides a gallery of screenshots and video documenting the disassembly of the MacBook Air and shows that it is relatively easy to access the battery, which is held in by a number of screws.
Aside from the innards being well designed, the disassembly of the MacBook Air was surprisingly easy. Hands-down the easiest Apple notebook we have ever taken apart. There's basically only one step to get inside the machine, just unscrew the bottom casing.