Hello to you Kcholzmacher!
Let's get you out of this rebooting cycle! Help is here! You have done so much troubleshooting and I really, really appreciate it!
Safe mode & hard resets are important to ensure it's not any glitches or applications causing the difficulties.
After you reset your phone did you add any applications back to the phone? More specifically any Task Killers, Battery Savers, or Antiviruses? These applications are known to cause system issues like reboots! If so, uninstall them and reboot.
If not, it may be the phone or battery as you mentioned. Is there any physical or water damage? If not we can replace under warranty!
Let me know.
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Yeah keeping a phone is a hot wet environment is not very smart. If the phone issues is due to moisture your warranty won't cover that.
Shut off the phone remove the sim and battery. reinsert sim and battery then restart. If that doesn't work you might need to do a hard reset or you may just need a new sim card.