Originally Posted by jusmee
Really, these devices use memory chips to store the data in cache, and I am sure you can't power up half a memory chip. Sleep mode has to maintain the same amount of memory no matter what.
That is exactly what I thought too when the idea of the size of the book's cache affecting battery life came up. Surely the whole memory is being kept alive by the battery when the device is in sleep mode, not just the portion of memory being used. It would be way too hard to figure out which parts of the memory are being used and to power just those parts (even if it was possible to power individual memory chips, and is there even more than one memory chip in the Kobo's?) Also, stuff normally isn't necessarily stored in a contiguous chunk of memory, it's common to have stuff all over the place as chunks of memory are allocated and freed by the OS.
Note I'm looking at this from a programmers perspective, I don't know all that much about the actual Kobo hardware.