A core is a pared down Farimon Chamber in a semi-standard form that resembles a beer keg or a vase. It has the same concepts: a lower-powered rune of fire with a crystal reservoir inside an iron container. It has a top that can be sealed closed.
When the core runs out of energy, it could either be brought into town to be recharged without bringing the entire artifact into town or requiring a smith to come out and recharge it.
⚠️ SPOILER: From this point, this page reveals spoilers for Flight of the Scions.
Kanéko sniffed and looked around. “What do we do now? Start the core? Compare it to the diagrams?” She gestured to the workbench and the plans for the water screw. The expensive plans she bought months ago from the back of an issue of Emerging Wizardry. It showed every part needed for the mechanism, but Kanéko and Jinmel couldn't get anything to work. On top of the diagram were their sprawled sketches of replacement parts, things they puzzled out, and random doodles.
“That thing is useless,” he sighed.
“Then,” she said hopefully, “just open the core?”
At Jinmel's shrug, hope rose inside Kanéko. She hurried over to the fire core, a foot-tall metal vase covered in runes. It was buried underneath a bag of moldy and scorched horse feed. She grunted as she shoved the bag aside. The vase was hot in her hand when she picked it up and carried it over to the boiler.
“Careful, Kan.”
“I'm not going to drop it,” she gasped, “again.”