Just FYI: it's very easy to inadvertantly switch the fan to "on" while you are carrying it, but not notice if it is in your bag. Power will be expended trying to spin the blade, but it won't spin if it is resting against something, whether it is your hip or the bottom of a backpack.
To prevent batteries being wasted this way, I make it a point to flip the battery over the wrong way whenever I put the fan away or pack it in luggage. This also will prevent small children from using the fans at inappropriate times.