Energon stars (also known as Energon chips) are supplementary portions of Energon that can be equipped by a Transformer for more energy. They serve as a convenient method to transport Energon and can also be used to summon a crafted Energon weapon. In addition, Energon stars can provide the equipped Transformer immunity to otherwise toxic or deadly Energon blasts.
Aurex 802.23 Alpha (US Unicron Trilogy Cartoon)
Energon stars were produced by raw Energon-tolerant races like the Omnicons or Terrorcons and were used extensively during the Fourth Cybertronian War in 2020 CE, though the Autobots and Decepticons quit using them shortly afterwards.
Primax 509.28 Epsilon (Wings Universe)
Much smaller forms of Energon stars were used in this universe not as a form of power but as a currency.