A better and cheaper option is a solar panel, 10 watt minimum in UK.
Other options are Nicro Day/Night Solar Vent, where the AirHead fan is integrated with a switch and used only occasionally.
We do not recommend use of any solar vent exclusively as all will at some point stop due to limited battery capacity. This may result in flying insects finding their way into the system by detecting the toilet itself.
Do not remove fan screen, this screen is very necessary.
A solar panel, (minimum 10 watt), may be added to counter effect the battery drain caused by the AirHead fan.