Went down a rabbit hole and discovered that iron-air batteries are a thing…
Each iron-air battery is about the size of a washer/dryer set and holds 50 iron-air cells, which are then surrounded by an electrolyte (similar to the Duracell in your TV remote). Using a principle called “reverse rusting,” the cells “breathe” in air, which transforms the iron into iron oxide (aka rust) and produces energy. To charge it back up, a current reverses the oxidation and turns the cells back into iron.
“Reverse rusting?” Weird. Interesting implications for power grid management, though.