I thought i would point this out, i was also under the impression that the screen took no power. as a test i left a page on since monday – the machine was fully charged.
anyways i took it out today to see if there was any drop and yes there is, the power is around 50% left.
so ive now set it to auto shut off, but i thought you might like to know it still does consume power albeit very low when the screen is on.
luckly it only takes a little while to charge so i can use it later to today.