The charging current of fast charge is large, so the charging time will be much shorter; The charging current of slow charge is small, so the charging time is long.For example, if you buy a nickel-metal hydride charger, which is marked with output current of 1.5A, this is fast charging, because the current 5 nickel-metal hydride battery capacity is more than 2500mAh (2.5Ah), with 1.5A current charging, about two hours will be full; If the charger you buy is marked with output current of 100mA or 200mA, it is slow charging, and it will take about twenty or thirty hours to charge the 2500mAh battery, and it may not turn the lamp after full (the current is too small to detect).As for the damage of the fast charge to the battery, it theoretically exists, because the large current charging heat is large, and the chemical material composition in the battery has the possibility of accelerating the life consumption. However, in order to save efficiency, this effect can generally be ignored (the battery cycle is generally 300-500 times, which can be used for so long is very energy-saving and emission reduction).