title_body: Kindle (classic) power consumption when reading PDF vs. MOBI
upvoted_answer: If the PDF file is not formatted to the size of your Classic Kindle screen (roughly A6 format or 6"x4") you will consume a lot more power because you will need to zoom in and out and navigate on the page in order to read it. A MOBI file does not have this kind of problem because it dynamically resize the text so you can read without interaction.
  
  Your e-ink device (any Kindle generation) will be off while you read and will power on when you click on any button or on the screen. So as well as it is on sleep mode it will consume less power. The device only needs power to refresh the screen and redraw anything or change pages, thus any interaction that redraws anything consumes more power.