I don't have a Kindle or Nook, I have a BeBook, but my problem appears to be universal to these readers as well. If I leave my reader in standby mode, the battery is dead within a few days to a week. But if I use it every night for an hour or so, I can make a couple of weeks on the same charge.
I have a Hanlin B/W book reader, and I enjoy it quite a bit. It changes pages rather slowly, but I learned to time it right so when I reach the end of the page it changes
I was playing around with a Nook at Barnes and Noble, I take it you like them a lot ? I was impressed at how slick and fast they operate. I was very tempted to pick one up last time I was in there. I am lucky it wasn't payday week