I havent used a stopwatch, but just in my case...
I read ebooks a lot and uses battery very slowly. You can easily read for a day without a problem.
Of course an emu uses batt much faster. Again I havent timed but usually I cant play a full day - if i guess, maybe i could play 4 or 5 hours? Something like that anyway. (Actually, I often play while plugged into my laptop anyway.)
Overall, I connect at least once a day to update podcasts and stuff, and the one charge is enough to give me a good day of usual use mixed browsing emu reading etc. I dont think I could do a whole day emu or a whole day video though.