S2 ENGINE

The Angels are powered by S2 Engines giving them unlimited power for an unlimited time. On the other hand, Evangelions are not designed to use S2 Engines however, during an expect chain of events, Evangelion Unit 01 was able to ingulf an S2 Engine within its body making the future need of Unit 01 for external power virtual moot (however the engine has to be activated).

The S2 Engine's power is so vast that during testing with Unit 04 in Nevada, USA, the whole facility (including Unit 04) blew up and was never found.