So, as an update, I think I have my Oasis settled to a pretty good battery life. I charged it yesterday, and unplugged it just before going to bed. I read for about 1/2 hour to 45 minutes before falling asleep, and then for an additional hour when I woke up. With wifi on and the light level set at 9, the battery went from 100% to 94%. That adds up to about 2% for ~30 minutes of reading, or about 25 hours per charge.
I'm satisfied with that
Shari