The usb port itself is not used for charging. It is used to read USB flash drives and transfer data. Can not provide the power required for mobile phone charging, the maximum power may only be 2.5~5W. So the charge is slow. Buy a car usb charger and plug it into a 12V cigarette lighter. That's enough power to power the phone.
To discuss the impact of mobile phone charging speed, we must first understand how the charging time is calculated. The charging time can be calculated using a simple formula: Charging time = coefficient (generally greater than 1) battery capacity (mAh)\/ charging current (mA). That is, when the charging current is unchanged, the larger the battery capacity, the longer the charging time; When the battery capacity is unchanged, the higher the charging current, the longer the charging time