Kindle Fire 7 Died - Need Battery?

It seemed to be holding a charge for shorter and shorter periods. I thought it might be because it was pretty full (8 GB) with maybe 30 books. But now it just stopped and shows nothing. I made the mistake of trying to attach it to the wrong size charge cord, but I didn't force it and I *think* it still worked after that. I've had it for 2 years and used it all the time. Is it truly kaput?

Thank God I have an extra one here, but still . . .

 

Explain. Was it the connector on the end of a cord or was it the wrong wall plug in adapter?

Buy a battery pack to charge if you aren't near a plug.
I own two 6,000mAh and two 3,350 mAh. The 3,350 (Vivitar brand) ones are small, lightweight and only cost $5 (US) at Target.

 

It was the cord for my phone, so the connector on the end was too big for the slot in my Kindle. But I didn't force it and the Kindle cord slides right in, yet nothing happens when I plug it into the wall plug adapter. (My wall plug adapters handle my phone and Kindle cords.) And I'm set up with a wall plug adapter and Kindle cord in 2 different locations and neither of them work. So it seems to be the Kindle itself.
Also, what about the fact that the Kindle would run out of juice after shorter and shorter periods prior to this?
Thanks for taking the time to look at this!