In general, there are two key factors that affect how quickly your device charges over USB: The maximum amperage of the USB socket or wall charger, and how your device negotiates power delivery from the socket/charger.įor a start, every charger or socket has a max amperage - usually between 500 milliamps (mA) and 1.5 amps (A). What that story doesn’t cover, though, is the variation between devices - why iPhones charge differently from Androids - and why two seemingly identical USB 2.0 (or 3.0) ports charge your devices differently. To begin with, you should read our story on how USB charging works, which outlines USB 1, 2, and 3’s specifications for charging, why some sockets and wall chargers output more power than others, and whether it’s possible to blow up your device by using a different charger (it isn’t). We will also be taking a look at a new device, called the Practical Meter, which finally gives us insight into the arcane world of USB charging. Why, for example, does an iPhone recharge quickly when you plug it into your MacBook Pro, but slowly when you plug it into your PC, or a non-Apple wall charger? Why does your smartphone charge quickly to start with, but slow down as it fills up? In this story we will answer these questions and more as we investigate the optimum methods of charging your USB devices as quickly as possible.

USB charging is shrouded in mystery - which is a bit ironic, given that almost all of us rely on USB charging of our smartphones and tablets on a daily basis.

How to use usb device with ipad