Energon cubes

The energon cube is the safest form of energon, used for transportation and storage.

Generation 1 cartoon
The energon cubes could be created by Soundwave, who generated the empty cube framework from his similarly-shaped chest; several other Decepticons were able to produce them as well. The Autobots were apparently unaware of them until their reawakening on Earth in 1984, when Hound described them to Prime as simply "some kind of cube". (Energon cubes were also shown to have existed by the time of Optimus Prime's creation at the end of Cybertron's Golden Age, but the technology might not have been widely used, or may have been lost for millenia.) By 2005, however, the Autobots had begun to use energon cubes for power as well.

Exactly how an energon cube operates is unclear, especially as their framework appears to be some sort of self-sustaining force field with no internal mechanisms. Most frequently, the empty cube is simply attached to or placed near the energy source from which it is to drain power, and the energy in question is automatically converted into liquid energon that fills the cube. Energon cubes have proven able to transform a vast array of resources into energon, including electricity, magma, oil and steam. Energon seems to have a much higher energy potential than carbon-based fuel sources: 1000 barrels of oil are needed to fill a single energon cube, and the electrical energy within the synapses of the human brain are insufficient to generate even a few drops.

The liquid energon within energon cubes is a glowing pink color, although the cubes could also be compressed for easy storage and transport, causing them to take on an iridescent rainbow effect.