Chosen Solution
I have recently cleaned up a Xiaomi redmi note 4X. It turns on and works with whatever charge is left in the battery. I think the shown battery level is incorrect. Stays green at 40% (with green led notification) It is not charging further. When switched off the led stays green as if it was charged, never over 40%. Ampere shows is consuming battery and not charging. It showed usb cable connected, but did not recognise it again after unpluging and pluging again. I fully discharged a replacement battery doing tests, it wont charge. Now I am working with the original battery which is at 40%. Any ideas?
Update: Red blinking light gave me a hint. I found some information on the protection diode of the charging circuitry. There seems to be a method to bypass the USBcircuit by plugging the charger first and then plugging the battery. Battery is now recharging fine. Still do not know the long term solution I do not seem to find any reference to the exact diode I should look for. Final update: The USB circuit was not properly cleaned from the back side, cleaned up properly and now it works.
