This is a simple clip designed for the stock 7.4 1000mah hard cased Lipo that comes with Fatshark FPV goggles.
The standard mounting method means the battery will frequently fall out of the elastic strap. This can range from annoying to down right dangerous especially if you are flying fast 250 FPV racers via the goggles!
The mount simply slides into the existing location on the elastic strap but stops the battery from sloping to an angle that will cause the battery to slide out.