Artron sphere

An artron sphere was a living ball composed entirely of artron energy, Bernice Summerfield thinking of it as a giant battery.

The Time Lord Magnus discovered the artron sphere inside the space/time vortex and managed to extract it into real-time. As artron energy was the primary power source of a TARDIS, Magnus set up a space station to tap into the sphere and drain it completely, gaining a near-unlimited supply of temporal power and complete mastery over the vortex; he believed it would begin "a new life for Gallifrey" and a new beginning for the "stagnant" Time Lord race. The First Doctor, in his later days, was against the project since its inception, the Seventh Doctor later thinking Magnus just "wanted to supplant Omega and Rassilon in the history books."

When only the core of the sphere was left to drain, it called out "STOP...PLEASE...," and the Doctor tried to reason with Magnus to stop, but he refused. Taking a staser from a Chancellery Guard, the Doctor blasted the station controls and severed the link, urging the artron sphere to go, which it did. (COMIC: Flashback)