dennis_arduinouser:
The arduino is used to send a signal to a motor driver. The motor driver is attached to the fan. I dont really know that much about consumption but the fan and arduino works when powered by 1 18650 battery or 16340 battery.
You should have told this in the beginning.
You cannot select a boost converter module unless you know how much current the fan draws.
Post a picture of your fan, that might help.