My daughter's 2-year old Samsung Galaxy Tab Pro 8.4 has been randomly and repeatedly restarting when it was not plugged in. I had tried all of the standard fix ideas found via Google and Bing (factory reset, clear cache, safe mode, uninstall apps) and none solved the issue. She primarily uses her tablet for Minecraft, Youtube, and reading books. When looking at possible replacements, the Amazon Fire was ruled out because no Youtube app. We didn't want to pay hundreds of dollars for a new Samsung (the Android skin is crap) or the Pixel C, so I was out of options, until I found a Youtube video showing someone changing the battery on this tablet. After watching that, I figured "I can do that!"
The repair went so smoothly it was scary. Using a Youtube video for reference and my iFixit Smartphone Repair Kit, I was able to remove the back of the tablet, remove the battery, and then add a new battery and close the tablet up in less than 10 minutes. After a night of charging, we are now a week in with NO restarts! I'm calling this one solved, thanks to iFixit and a new battery.
Find videos online or a good guide here on iFixit. Also, make sure you won't be devastated if the repair goes wrong. We were prepared to write this tablet off if I couldn't repair it or if someone happened that ruined the internals. Luckily, we didn't have any issues.