With less than 10 minutes of use with 3g to download books and at all other times turned off, I get approximately 10 days use from full charge to the warning pop-up on my screen. This is with moderate use of approx. 2-3 hours reading daily.
However, this is when using the Kindle 3 cover with light 100% of the time. I think 10 days' use while the booklight is pulling power directly from the Kindle is outstanding and I have absolutely no complaints. I was in the "never will buy a Kindle" boat for quite a while until I heard about this cover with light that requires no separate batteries. That is what hooked me and although there are a couple things that drive me insane about the Kindle (lack of a true management system
) I still use this over all my Sonys now.
That being said though, if Sony were to come up with the same type of lighted cover, I would jump right back to them. Sorry, but true!