Xiaomi fast charging line charging slow down may be due to the following reasons:
1. The output current of the charger or power supply is insufficient, it is recommended to replace the charger with more power or replace the power supply;
2. The charging cable is damaged or aging, it is recommended to replace the new charging cable;
3. The mobile phone or charging port has dust or impurities, it is recommended to clean;
4. Mobile phone battery aging or insufficient capacity, it is recommended to replace the battery or battery maintenance. Check and resolve the problem according to the actual situation.