[HTC 10 Questions & Answers] HaiderZeus:
Hello everyone, I have faced quite a confusing issue on my HTC 10 and here are the details:

I have owned this HTC 10 for 3 years and it's been running like clockwork all the time no matter what I threw at it. It's battery life dropped significantly, but other than that the device has been great. I never rooted it or unlocked the bootloader. It's been running on stock OS from HTC all the time and I never manipulated that. These are the device information:

OS: Android Oreo 8.0 stock from HTC, installed on Jan, 2018 via the official OTA update I received at the time.

OS Build: 3.16.401.2

S-ON

A few weeks ago, I left it charging while it was in extreme power saving mode. Not the first time it goes to extreme power saving mode automatically and not the first time I charge it while it is in that mode. I left it charging for a bit longer than usual as I got occupied and forgot about it. After about 10 hours give or take, I went to take it off the charger to find it stuck in a bit of a strange boot loop. So the device boots up normally getting through the splash screen and HTC animated bootup logo. The lock screen comes up. I can unlock the screen normally. Both the pin and finger print scanner work fine. Once I unlock the screen I find the device in extreme power saving mode even though the battery level is above 80%. When I try to exit from extreme power saving mode a crash pop-up message comes up telling me that "Battery has stopped working" and it asks me if I'd want to send an error report. About four seconds after that an other error message stating "Setup has stopped working" comes up and three seconds after that the device reboots and the whole thing happens again. If I don't attempt to exit the extreme power saving mode that "Setup has stopped working" error comes up too and the device restarts. If I don't unlock the screen I get that error message on my lock screen and the device restarts. So basically it is stuck in that loop now and it keeps restarting.

I can access the download, recovery and fastboot (bootloader) modes normally. I did a "Wipe cache partition" from the recovery mode multiple times, but that did not help. I tried to take off the sim card and bootup the device and it did not help either. I tried booting into safe mode and the same scenario occurred and the device got stuck in that same loop. I contacted HTC support and they have not provided me with any useful or new solutions so far.

I have not backed up the device in a while and I have some important data on it, therefore I would like to avoid resetting it and wiping the internal SD by all means.

I do not have any sort of a task manager or a battery management app installed on the device. I have not installed any new apps on the device in a while either. I did not notice any drops in device performance or any other issues before this. So, I think this issue was probably caused by some bad updates to some core system apps (probably the battery app), that were installed automatically while the device was charging (as that happens by default).

I think if I could get the latest official stock OTA update for my device and flash it from SD card, then that might fix this issue. Unfortunately though, I do not know what my CID is and I could not acquire it by using SDK, adb and fastboot tools as the device USB debugging is turned off. I tried to find a way to turn it back on from PC or from the few seconds I have with the device on, but so far no luck. When I plug in the device while it is in download or fastboot mode, adb tools does not recognize it at all, but fastboot does. However when I run the command "fastboot getvar cid" I get nothing just "cid: " like this with no value. And when I run the command "fastboot getvar all" I do get the values of many variables that include information about the bootloader and other device information, but I do not get anything that mention the CID.

I also tried to use some of the dial up codes that give device information hoping to get the CID, but none of them seem to work. Nothing happens when I enter them, they just vanish without returning any values.

If you have any idea about how to solve this issue while maintaining the device data and avoiding to reset it, then please let me know. I am open to try advanced complicated solutions as well if any would help me to resolve this without losing my data. I will appreciate any information or feedback you can provide.

If you would like me to provide any more details that I might have missed, please let me know.