I am not saying that it draws 500mA. I suspect it is like any digital processing device that it draws more when the processor works hard and more when the display is on. 500mA is just to provide the headroom for the peaks of power consumption, so it doesn't run out of juice.
But it is not purely digital, the inputs and outputs are analog. If it works really hard and you don't have the headroom, its power level may become unstable and erratic. That is a good way to achieve unwanted noise in the analog circuits.
I'll try changing out the batteries when I get home today. I forgot the bat life isn't that great.
