Xiaomi Vacuum Mop 2 Pro+ automatically charging but battery level not increasing

The robot is functioning normally. However, since the battery level fell below 15%, it automatically goes to the dock to recharge.

After it finds its way back to the charging dock
1. The robot says "charging" as seen in the video
2. The robot's lights are blinking indicating "charging" status
3. Xiaomi App shows that it is charging

But the battery level does not increase at all.

Solutions tried:
1. Cleaned the charging dock
2. Cleaned the bottom part of the robot vacuum
3. Plugged and unplugged the charging dock
4. Reset the robot - in the app
5. (lastly) Factory reset - long press power button and reset button

It doesn't clean anymore since battery level is below 15%. Firmware update unavailable since battery is below 15%. I did not open the battery pack below, as there was a sticker saying that the warranty would be void if sticker is removed.

After factory reset, the battery went even lower (9%) and does not increase at all even if it says it's charging. Help. :(

Видео Xiaomi Vacuum Mop 2 Pro+ automatically charging but battery level not increasing канала Da'vinC