My kindle battery lasts for about 18 hours, I had it shut down due to lack of power just when I was in a good and exciting bit of a book and had to wait a couple of days for the power to come back on and then recharge the kindle.
I've looked at things like book box at our library, it's not very good, you can wait months for a lot of books and the numbers they have seem to be limited.
Many of my books are out of print, or are more expensive to buy as e=books than they are second hand. I'm certainly not going to buy a non fiction e-book for a couple of pounds cheaper than a hard copy, when I'm not going to be able to see things like maps properly as they're an important part of explaining what I'm reading about. A couple of authors I read, whilst their books are in English they're set in other countries and I want to go back to the page that gives the pronunciation guide, this is far easier in a real book than an e-book.
Another thing I'm finding is that I sleep better if I read a paper book, than an e-book.