ipad air 2 shutdown

I have seen others posting a similar problem though I haven't actually seen a reply with a definitive solution yet:

My ipad air 2 shutdown while i was playing a game yesterday. It went to a backlit black screen, then shut off. Plugged it into power and it showed a tiny red sliver of battery, which was odd because i was pretty sure it has been closer to 80% when i was using it. Restarted it and it showed battery life of 60+% just moments after plugging it and and seeing the red sliver. Checked software update; updated to 11.2 and went to bed.

Today the same thing has happened twice more, once when using a book-reading app and once playing a diff game. Both times the ipad was unplugged but the battery was in the 80s% despite showing red sliver when i had to plug it in to turn it back on.

Anyone??