Because the phone's data cable and charger are damaged. Xiaomi's K30 is charged less and less, which is usually because of the phone's charging data cable. The legendary current power does not meet the standard of charging, resulting in less charging. That is, the data cable and the charger are damaged.
The reason why the Mi k30 charge less and less is that the use of computer USB interface or non-original charging device charging, will also lead to slow charging, it is recommended that you use the original charger to charge the phone. Click here to find out how to tell if your phone is in fast charge mode.