Impulse capacitance celledit this page

From Memory Alpha, the free Star Trek reference

An impulse capacitance cell is an energy-storage device connected to the impulse drive in starships such as the Intrepid-class. It holds enough power for a single short impulse burst during emergency situations.

In 2371, B'Elanna Torres released power from the USS Voyager's impulse capacitance cells into its driver coils, in the hopes of breaking free from a magnetic wake generated by a swarm of space-dwelling lifeforms. (VOY: "Elogium")