I do NOT have an extended battery or back cover.
What I have or had been wondering is if it was a battery issue, not an extended battery issue. Meaning if a battery, extended or regular, had some sort of issue, it would cause these problems.
Here's what I tried after a couple weeks of having endless reboots and black screens. And none worked.
-Factory reset.
-Factory reset then not installing any apps.
-Factory reset then not reinstaiing any apps, making phone calls, sending text messages, browsing the web or using any of the pre installed apps.
-Different chargers
-Rebooting before charging.
-Battery pull before charging.
-Rebooting after charging
-Battery pull after charging
-Leaving the phone on the charger until I needed it.
-Removing the phone from the charged once fully charged.
Once I swapped the factory battery back in, the issues pretty much stopped. Only one random reboot since October 27th. And no locked black screens. On November 4th I upgraded to the first leaked system version update (5.5.886). Form that afternoon unitl Monday, November 7th I had no reboots or black screens. On the evening of November 7th, I installed the second (5.5.893), then third (5.6.893), then fourth update (5.7.893). I also reinstalled the extended battery. And so far, no issues at all.