Doesn't seem that way
“How do you do it?” he asked, ignoring her question. “How do you recharge them? Wait. You put something else into them, something to be burned away by the sunlight? That temporarily blocks the circuit—or offers resistance to it.” “Some heat from a local works,” she said, studying him. “We have a few captives. They prime the sunhearts with a little of their heat, then we leave the sunhearts out. It works. Use some special Investiture instead, and you get a corrupted cinderheart to make the Charred.”