To recalibrate, run the battery down totally. Play a movie at the brightest level, run a bunch of Apps in the background, etc. Get it to the point where it shuts off on its own and no juice in the battery whatsoever. Then plug it in and let it charge up over night. I charged mine for 12 or more long hours just to be sure it had a full charge. After that, reboot the iPad by holding down the home button first then the off button on top until the screen goes blank and the white apple logo shows up on your screen. At that moment, you can release these buttons to allow the iPad to boot up all the way.
Then you can use your iPad and see how it works over the next few days. If its still not holding a charge even when its in sleep mode, you may want to make an appointment with your local Apple Genius bar and have them do an assessment and diagnostics. I just remembered that my iPad Air 1 was giving me trouble at first as well. It would not charge up to 100% It would only charge to 99%. Apple told me to recalibrate and it was fine after that.
Here's a lesson about rechargeable batteries: whenever you get a new device that has rechargeable batteries, do not use it right away. Plug it in and charge it until its fully charged. Better yet, run the battery down and recalibrate it. The device may have been in stock all this time starting out with a 100% charge from the factory but then lost some juice while it was in stock before it was sold to a customer. Remember, these iPad 2 Air devices didn't come off the conveyor belt and into the stores. They've been sitting in stock for a while somewhere until they officially rolled them out to the stores for their customers. So, many of them may have lost some juice just by sitting in stock.
Hope this helps. 🙂