Low Battery keeps coming up on screen when it is showing 100% charged
I Have an iPad Air (2) that functions for less than 5 minutes unplugged (showing 100% charge by the battery icon), then will just wink off. It gives no warning. It just shuts off. It does not reboot. As soon as I plug it back in to power, the screen lights and shows a large icon showing a drained battery icon in red on a black screen indicating a 2% charge. Once the iPad boots under power, it immediately shows that the battery is 100% charged by the small battery icon at the top of the screen. I can only operate it while it's plugged in, and it won't take a charge when it's plugged in, because the iPad says it's 100% charged. This is an iPad Air (2)and I have just upgraded it to iOS 12.4.6 I can no longer use it unplugged, so is there a possibility that the battery has reached the end of its life cycle? It was given to me for my 70th birthday 5 years ago and until December last year was working perfectly. I regularly clear the photos, emails and messages and it is only half full. Anyone else have this problem or have any suggestions? Thanks for any advice or help you can provide.
iPad P
iPad Air, iOS 12