If the USB port are specified as handling charging of USB devices then it is ok, but laptops seldom have those kind of ports. Scanner draws 700mA and charging an additional 700mA.
In the USB 1.0 and 2.0 specs, a standard downstream port is capable of delivering up to 500mA (0.5A); with USB 3.0, it moves up to 900mA (0.9A). The charging downstream and dedicated charging ports provide up to 1,500mA (1.5A).
/Ubbe