Life Energy

Life Energy is the very energy of living organisms. It is never explained what exactly is Life Energy other than the fact it is life itself. It could consist of various organic energy such as bioelectricity, body heat or based on various esoteric energy philosophies such as Qi, Mana or Vitalism.

Sonic the Hedgehog
Dr. Eggman's most earliest models of robots were powered by life energy. They were known as Badniks and were powered by small animals which trapped the animals inside themselves while all the while drawing energy from them to stay active. However a hit could easily destroy them entirely harmlessly freeing the hostage within them.

Sonic Lost World
Dr. Eggman restarts his Badnik series on Lost Hex which, like before, powered by living animals, and shows the process of how the animals are "robotisized" into Badniks (Simply taken out the capsule and drop inside a vacant Badnik). Dr. Eggman also constructs a machine known as the Extractor which, like his badniks with single little animals, is able to draw the life energy of the world itself and condense it into a green liquid state. Cubot, despite being a robot, is able to drink the substance and enjoy it as it is the same form of energy that powers Badniks only in liquid state. The machine however was made only to syphon off small, harmless amounts of energy from the planet while the Deadly Six take it to extract all the life energy from the world.

Trivia

 * In the British comic Sonic the Comic the victims that powered Dr. Robotniks badniks and robots were reconised as organic batteries. The robots who take them appeared to be active but at limited capabilities until it takes in a victim. Sonic had to be careful fighting Badniks due to them being hostage.
 * Life Energy can be compared to Ki from the DragonBall series. All life in the series possess some degree of the energy which, to those who know how to manipulate there own, can use it in powerful attacks or contribute it to other powerful attacks like the Spirit Bomb. However, unlike the DragonBall series, Life Energy is used and regarded just for living while Chaos Powers can be more comparable to the kind of techniques seen in the DragonBall series.
 * The world life energy can be compared to the Lifestream from Final Fantasy VII in which it is the essence of life of Gaia itself which can be extracted in a green liquid energy state known as Mako energy.