It doesn't transmit IR for each LED flash, so the theory in #9 isn't correct, but I think the single pulse of IR you get when first pressing the power button is longer with the low batteries than it is with new ones, so it's just possible it is sending something as well as the 'power' code. Although it could just be that the lower voltage is messing up pulse length
EDIT
Iv'e just realised that as the 'Mode LED' thing only happens on a power button press the Humax (or TV) is being turned off, so it wouldn't be able to display a low battery icon anyway - Ah Well ! !