The USB Implementers Forum (USB-IF) has released a new battery charging specification which defines how devices should draw current through USB from wall chargers or PCs.
The Battery Charging Revision 1.0 specification defines a mechanism for devices to detect whether they are attached to an AC charger, host or hub. It was devised in response to the growing trend among mobile devices to use USB for charging capabilities.
If a gadget is plugged into a high-powered port, it is now allowed to immediately draw currents in excess of 500mA. When connected to a PC or hub, portable devices must limit their current to 2.5mA, 100mA or 500mA, as required by the USB 2.0 specification.
The new standard also includes a provision to allow portable devices with dead batteries to recharge at 100mAh even if they are not able to power up.