I had my first macbook's battery replaced. I took it into the apple store for an unrelated problem, the tech noted the awful battery life and asked me how old the laptop was, said, "that's not right...," and grabbed another battery. Nice and easy.
If I remember correctly, with the Macbook Air it will have to be '"that's not right...", and grabbed another Macbook Air, and started migrating my data, etc, etc...'
Nope. Had a battery replaced in my 2012 Air recently(only because a clip separating the battery from the case broke,not because of the battery life) and it took 30 minutes to get it done at an Apple Store.
The RAM is the thing with Macbook Air's that permanently soldered to the system board. Everything else is difficult to replace due to the form factor, but still replaceable.