I leave wifi on now on all my kindles. I just like the sync to work always. Just the way I roll. Same with my Oasis2. I used to keep wifi off, but for me, its not really that big of a difference. I think because of the amount I read, I have to charge it at some point no matter if wifi is on or off. And I have put it down with wifi on for a while using a new basic I got and it didn't go down a lot while in deep sleep.
So I just plug it in when it looks like it needs juice. I don't time anything anymore. I have never had a kindle last me more than 4 days period. I can read a book a day, sometimes more.
But my Oasis 2 even with reading a lot can still go 2-3 days I think. I really don't know exactly as I don't time it anymore. But that is hours and hours of reading, especially on the weekend. Pretty sure it gets what it claims on the page when adding the so many hours per week and translate to actual reading time.
My voyage lasts a wee bit longer and so does the Oasis1 in the cover. The basic I don't know yet. Overall, not that big of a difference between them. But then I remember the days when I had to read while plugging in my K1 as it barely last me through a day reading heavily.
So my Oasis2 is operating as it is suppose to. Counting actual reading hours, not days, actual usage. Which is really what matters to me at least. Not saying some of them can't have issues. Mine doesn't though thankfully. And I wish all my devices charged as lighting fast as this Oasis2. My phone can take 4 hours if I run it down, but it does have a 5000something batter, so its huge. Oasis2, I plug it in, do some stuff and its green light. Fast. And I like the buttons and shape and screen and I like reading on it.