7.4V batteries were used in earlier days of the saber hobby before Neopixels for certain older in-hilt LEDs ex Luxeon V that required high voltage and in some circumstances for running 2 dies of a tri or quad LED star in series where high source voltage was also required, instead of parallel wiring more common now where current is divided instead of voltage.

So originally soundboards incl Crystal Focus were designed to be ABLE to handle high voltage for such applications.

Today a single cell battery solution of lower voltage but that can sustain a high amperage current draw without tripping the protection PCB like a good 15A 18650 is used for modern saber applications and is what you want, especially for Neopixel.