i read on my Kindle an average of 5 hours a day, give or take. after 7 days the battery is way past the halfway mark. my wifi is off. i have over 100 books on it.
i think it's safe the month long things was an advertising smoke screen. it'll probably last 1 month if you just look at how pretty it is in its case on the shelf
but i can't say i'm disappointed. one week is plenty of autonomy.
too bad you can't take it on a desert island. __sigh__