Hello
I am a phone repairer, I French, excuse my English because I use Google Translate
I also have a Xiaomi MI5 with this problem. But I have (almost) succeeded in solving it:
I removed the back cover of the battery with a super thin metal plate. You can also use a suction cup to create a space for a guitar pick to insert the battery cover.
Next, remove the 9 screws from the cover that protects the motherboard. Be careful, the screw next to the camera is not magnetized, make sure that it remains.
When you have removed the 9 screws, and removed the protective cover from the motherboard, unplug the appropriate bat- tery from the battery. It is located at the bottom left of the motherboard. Reconnect it, and connect your phone to your outlet, trying to recharge it. Normally, the red notification LED should blink to show that your phone is charging.
If it goes well, you just have to do everything again, and close your phone again.
If this does not work well, unplug the battery pack again, and the bottom right-hand tab, corresponding to the charging connector. Reconnect them and test the charging again. Normally it should work.
If it still does not work, unfortunately, see directly with Xiaomi.
I think it's a battery issue, which is no longer powerful enough for the phone. I removed the "second space" which takes a lot of battery, and since it has not planted anymore. I bought another battery, and I will test later, see if it solves the problem, and I will keep you informed.
If you have any questions, do not hesitate.