The Supercharger is an add-on for the Prime and PRO series of underwater flashguns made by the Slovenian manufacturer Retra.
The Supercharger doubles the battery life and reduces the recycle time by more than 50 percent. It is powered by four AA-sized rechargeable batteries, making the complete set (strobe and add-on) running on eight batteries in total.
In addition, it acts as a helpful grip for strobe positioning underwater. With this add-on attached, the technical specifications of the Retra strobes include a recycle time at 40% power output of ~0.7s and the number of flashes at 50 percent power output of 700+. The combined (strobe and Supercharger) assembly weight is 1150g.