Power pack

A vital component used to store energy, without which a Decepticon or Autobot cannot survive. Also used to amplify the abilities of particular robots. The Protectobot Groove, for instance, acts as a power pack when his group forms Defensor. Though each individual member contains a power pack it is his function to provide Defensor with a high enough level of energy to create his powerful force field.

From Teletraan I: The Transformers Wiki, a Wikia wiki.