S² Engine

An S² Engine, or "Super Solenoid Engine", is the organ within Angels which grants them an infinite power supply. Evangelions do not possess S² Engines (alternatively called "S² Organs"), and thus can only function without external power cables for about 5 minutes of internal battery power.

An attempt to install an S² Engine in Evangelion Unit-04 at Nerv's second branch in Nevada resulted in the disappearance of Eva-04, Nerv-2, and everything else within an 89 kilometer radius of the base.

However, the S² Engine research data was preserved in Germany and the project was continued. Ultimately, the Mass Production Evangelions would all be outfitted with S² Engines.

Evangelion Unit-01 was eventually able to obtain its own S² Engine, when it went berserk and physically devoured the body of the 14th Angel, Zeruel, and consumed the Angel's S² Engine, thus essentially becoming a living God.