Here's why:

* Cellular Respiration: Mitochondria are the powerhouse of the cell, where cellular respiration takes place. This process breaks down glucose (sugar) and converts its chemical energy into a usable form called ATP (adenosine triphosphate). ATP is the primary energy currency of the cell.

* Energy Storage: While mitochondria don't directly *store* energy in the way that a battery does, they are responsible for producing the energy that the cell needs to function.

Let me know if you have any other questions about cell organelles!