What could be the reason for turning off the phone?

Question

Mobile devices

Good afternoon.
I know that the Internet is filled with answers to questions of the level: “Why is the phone turning off?”, “The charge is 50% and the device turns off, what should I do?” etc.
For myself, I did not find the answer to these questions, because my problem is as follows: about a month and a half ago, I unsuccessfully dropped the phone, picked it up and everything remained as it was in its place. Along the way, I bought a Power bank for 10000mAh and found that there is no 3000mAh there either. I continued to use the phone and at some point it started to turn off and at 70% and at 90% it even happened. And after turning it on again, I continued to use it, but when it turned off again, after turning it on it showed 0% and after that it did not work at all.
So, tell me please, what could be the problem? Did the fall play such a role, or did the wonderful Power bank disable the battery. It’s not that it’s a forest for me, but there is one thing: if you use the phone from the network, then it works like it was bought yesterday, otherwise it starts to slow down, as if it is on energy saving and the battery begins to live its own life.
There are several nuances:
1. I am familiar with the calibration and tried to carry it out, but I did not notice success, although after charging it from 0% to 100%, it turned off once.
2. I am familiar with flashing and thought that it was in it, although it was too stupid, because it served me for half a year and the battery held up remarkably. I note there is the fact that I changed the firmware, thinking that it was the case, but as it turned out, no. Everything remained in its place.
3. Malware? Unlikely. A couple of instant messengers and a browser.
4. So I don’t understand, it turns out that the fall played a role or what? Why does it work from the network without disconnecting, and so it turns off and the battery does not last long?
5. Battery controller? Phone fee?
Phone model: Meizu M5 NOTE.
I tried to describe the whole essence in as much detail as possible, I hope it didn’t turn out too clumsily. Please, do not throw stones and do not advise to run to the service center, given that I know what service centers we have in the city: “I farted in one corner, and in the other they will say that I crap.”
Thank you very much.

Answer 1

You explained the essence of the problem in great detail, but apparently no one who read the post has the necessary knowledge to help solve it. I am no exception, but I can advise you a resource where first-class phone repair shops are presented. You will find their addresses and phone numbers right on the site, along with all the useful information. By the way, you can also use free diagnostics. They work with all popular manufacturers and use only "native" components. Here https://www.golaika.ru/remont-telefonov/ I found an expert in my field and was very pleased with the quality of the repair, service and price.