Ipad air 2 blinking red battery and charging with lightning bolt

This is the usual icon for when the battery is drained. If it's totally drained, just plug it in and it will eventually turn on after several minutes.

Now another answer for a different situation. I had an iPad Air where the red battery icon would come on even when the iPad had a charge. I think it's a glitch that may happen when the iPad is overcharged. A few times I was able to get it working again by restarting the iPad.

With the iPad connected to the power supply, I would do a restart. Push and hold in the Power button and the Home button at the same time until the iPad restarts. The screen will go dark and then the white Apple logo will show up. Then release the buttons.

If the Apple logo doesn't show up after a few seconds, keep the buttons held down. Sometimes it took two or three cycles of continuously holding down the buttons until it pops on. It's almost like it's cycling through the software to find a way on.

Critically low battery - requiring charge. If your iPad is connected to your charger, perhaps your charger, cable or power-outlet are faulty.