Actually, Dan, if you've got that thing handy...

Does it happen to have Word on it?

If so, and if you have access to it, do me a favor and open up *just* Word, showing a 20-page document in full screen reading mode. Let it sit there, ideally with a bluetooth mouse connected. Screen brightness can be turned down a bit, but it must be set so that it does not go to sleep nor have the screen turn off at all. How long does its battery really last in that state?