Never - not unless youm going away for a few days without yo 650 [why would you ?], - never power off,or leave "open" on page you 're reading,but put in sleep mode when you finish reading each night. Holds charge better ["educates" the battery] and actually improves battery life etc...
Then, of course, it won't take so long to to re-enter books - cos it doesn't have to anyway- and will open on the page of the book you stopped reading on.
And use a wall charger - quicker [ you can leave it on overnight, can't "overcharge" it}, and gives a better charge also.
