I think weatherman hit the nail on the head. It all depends on page turns, of course and the manga I was reading did lead me to turn pages a lot more often and on top of that it was in PDF and each page is a picture: the whole battery-draining trifecta!
I did notice that my kindle charged when I connected it to my iMac so that's good. Another strange thing I noticed is that the battery icon changed when I changed the text size. So, I went from size "3" (the middle of the 5 available sizes) to size "2" (one size smaller) and the battery icon now shows more juice available. Of course, this could just be a glitch in the battery refresh or it could be that the Kindle shows available battery life according to the size of the text: smaller text means fewer page turns which means larger battery life available?
weatherman, you said ... about 1.5 hours each day for a couple of weeks. So, that's about 20-24 hours of reading time which makes sense with that I have been seeing. I read a lot more than 1.5 hours each day and so it makes sense that my battery would be used up more each day.
Thanks everyone! It's good to hear that my Kindle DX is most likely not defective and that I won't have to send it back. I love it!!!