Charging phone from laptop using USB cable - why is so slow ?
Why does phone charging from laptop using USB cable take so long ?
Charging the phone from PC using USB cable is slower, because USB port has lower amperage than standard charger plugged in the socket.
Charging phone from laptop using USB cable takes hours, because USB 2 provides 5 volts / 0.5 amperes and USB 3 can provide 5 volts / 0.9 amperes.
Depending on phone model, the standard charger can provide 5 volts / 2.0 amperes.