I leave WiFi ON all the time on my Voyage. I rarely even open the the darn thing to read on it and it mostly sits on a shelf collecting dust. It might be three or more weeks before I open it up and see if it is still charged, and it always still has enough of a charge to turn ON. I charge it about once a month. If your Kindle is left at home mostly, then no need to worry about WiFi drain on the battery. If you are taking it out away from your WiFi, then it can be an issue as it will search for networks to join.