One of the best purchases I have made - have used the Ryobi fans all day at dog shows - easily 6+ hours.  They move a ton of air and make a huge difference.  Lab breeder at recent show had one on each of her 4 crates in her truck and all her dogs were cool and compfy despite the heat & humidity.  Also many competing in agility have the Ryobi fans.  Of course more expensive initially buying the fan + charger + the batteries, but so worth it and maybe the best part is no more small crappy crate fans and D batteries!!  Doesn't take long to put a full charge back on the battery for the next day.