I have run into an issue after owning my tablet since early 2016.

I seem To have run into an issue after owning my tablet since early 2016. It's begun to charge very slowly and discharge very quickly. More recently, however there's been a larger issue. After running around for a day, I got home, pulled my tablet out of my bag, and turned the screen on. I then noticed something very odd. The battery indicator was showing 0% (it was 58% not even 30 mins before) and the lightning symbol was showing up in the icon, as if it was charging. It wasn't plugged in at all. I tried restarting the tablet after plugging it in, and was greeted with the dead battery icon. This persisted for close to 2 hours, until it finally started charging. After turning it back on and charging it for close to 14 hours, the battery was only at 85%. Now, it still has the symbol that it's charging while unplugged, however, it's flashing now. It won't let me turn off the screen, as every time the charging symbol appears, it turns the screen back on. Is there any solution to this or is this the beginning of the end for my tablet?