The power cell is an important precursor artifact in Jak and Daxter: The Precursor Legacy. They primarily functions as an energy source, much like a large battery. A power cell, when active will hover slightly above the ground and four separate pieces of it will fly around the main piece in a manner resembling an atom. When picked up they revert to a normal ball state until they're put to use again. A power cell can fit in an open hand and glows constantly when active.
It functions as the main collectible in the game, where they are needed to power items to reach new locations and forward the plot. Jak first needs 20 for the Heat Shield, then 45 for the levitation machine and finally 72 for the heat shield upgrade. However, to unlock the Secret Ending you need 100 cells (you can miss one since there are 101) to open the door leading to the Rift Gate. They are scattered around the world and Jak has to find them or trade them for Precursor Orbs (90 for one cell) with the villagers (though Oracles request 120 orbs).