I have a mid-2012 MacBook Air, and the Service Battery alert is showing My 13" Macbook Air recently started showing the "service battery" alert. It's the mid-2012 model, and is still under Apple Care. The alert seems to appear mainly when I'm running off the battery. Is this a battery issue or a bug in the system?
If it is still under Applecare I would absolutely get it checked out.  In the very least if there is an issue, you will get the battery replaced under warranty and be able to enjoy a few more years with it.