The Three types of Hero Core and one uncharged Hero Core.
Furno's core being charged.
A Hero Core is the personal power source for Hero Factory Heroes. They are made by the precious Quaza Stone which can only be retrieved by Hero Factories founder, Akiyama Makuro.
Once a rookie is made, the Hero Core is put in their body and it is charged, this happens in the Hero Core Room. Once all this is done, the Hero is alive. If the Hero Core is taken away from a Hero they will automatically shut down. It is advised that after each mission the Hero charges his or her core. Once the rookie is felt to be ready to be a fully fledged Hero they are taken to the Supercharging Facility and are transformed. A Hero is not allowed to go on a mission if their Hero Core is drained, they must go to the Quaza Chamber and get their cores charged.
Makuro holding Furno's core
The oddest thing about the Quaza chamber is that it seems only one hero at a time can use it. As proven during the Corroder crisis, Stormer was prevented from getting his core recharged because Furno was already in the chamber. Since there are so many heroes produced each day in the factory, it stands to reason that every hero team (along with the rookies assigned to them) are allowed to use only one Quaza Chamber per group.