A cautionary tale:
My Kindle Fire split across the top backing and the screen a few months ago, although it was still working. I thought I had been clumsy when it was in my luggage during my summer travels. Finally decided to go to Best Buy to have their in-house Geek Squad check it out, and found out that it was actually my lithium battery that had swelled up and caused the split. Definitely unsafe.
The tech explained that it can happen if you leave it plugged in all the time - yes, I'm Guilty, I left it plugged in for my convenience to use while I watched TV but apparently lithium batteries don't like that.
Bought a new Fire HD8 for about $85 so it was not an expensive replacement, but I wanted to pass on this story to any others who may be as clueless as I was about this.