When charging, measure its charging current, such as the actual charging current is one-tenth of the capacity of the rechargeable battery, it is slow charging (that is, standard charging); If the charging current is close to or greater than the capacity of the rechargeable battery, it is fast charging. Example: a rechargeable battery is marked as: 1.25V, 500mAH, when charging it with a charger, if the actual charging current is about 50MA, it is slow charging. Now the chargers slow charge less, most for fast charging.
Generally, 5v2a and above are fast charging, that is, charging power above 10w, such as 9v2a, 5v4.5a, and so on.