This is just another simple, dual 18650 battery case to fit FPV goggles, but, it has a separate compartment for a single 500mah lipo cell that powers the de-fogger fan on my Skyzone Goggles.
The fan I have turned out to be a low voltage fan, which I didn't realize until I connected 8V to it.... Sounded like a Boeing trying to take off !
Also, it's nice to have the fan running from it's own battery without adding to the power consumption from the main batteries .
Use it, don't use it :)