ipad mini 4 automatically shut down (full battery)

Hi,

My ipad mini4 is updated to the newest version. Recently, it often shuts off automatically even when the battery is full. Then when I try to turn it on for the first time, it shows that it needs to be recharged. However, when i again try to turn it on, it will turn on and the battery will drop a few. Sometimes, I can again use it normally. But sometimes it shuts off again. So I have to repeat this process several times until I can use it normally.

What's the problem? Battery? Or system?