Nexus 9 doesn´t turn on

Hi,

I have a Nexus 9 HTC 32GB. Last year at some point the tablet turned off while there was still battery left. After the first time I was able to get it up and running again by charging it a whole day long. But then it happened again.

I tried charging it with the original charger, via USB and wallplug, also with a more powerful Anker charger etc.

What happens now is that when charging at some point the boot menu appears but before I can choose any option (HBOOT etc) it turns off again.

I red that this could be a problem with the battery where it was damaged while it has been completely empty.

I would repair it if I could be sure it must be the battery. Can you imagine something else being the root of this problem?

I always updated the operating system.

Thanks in advance