iPad keeps charging and uncharging
iPad Air 2 and iPhone SE have different power adapter (head charger unit). iPad Air 2 needs 10W adapter, while iPhone SE needs 5W adapter.

In my experience, I can use 10W adapter for charging my iPhone 6 (which using same adapter with iPhone SE and some users said it will boost the speed). But iPad Air 2 can not be charged with 5W adapter, because it will need more power.

If you have used the correct adapter, make sure there is no problem with the USB cable and your iPad USB port. Because sometime, dust and dirt can disrupt the charging process.

Check this page to identify your adapter: https://www.apple.com/power-adapters/