They do not list the current drain so hard to qualify
Max power = 5 V (USB Voltage) * 0.5 Amps (Max Current provide by USB2) = 2.5 Watts. So since it is not going to max out the USB port Power consumption would probably be less than say 2 watt/hrs added drain on battery
Best quess (and totally a wag) probably decrease total battery time by 15 to 20 min.