Form Energy, which makes iron-based batteries to hold electricity for days, said it raised $750 million to expand production. That follows a $550 million raise by rival Antora, which snagged the same amount to accelerate production of its thermal batteries made from carbon blocks that also hold power for at least 100 hours. Unsurprisingly, data center power demand underpins the investment spike.

Form, which began shipping its iron-air batteries this year built at its Weirton, West Virginia, plant, said the latest round, led by T. Rowe Price, boosts its total funding to $2 billion. The company didn’t immediately provide a valuation figure with the latest funds, though Pitchbook estimates the deal values the Somerville, Massachusetts-based company at $4.3 billion. Sunnyvale, California-based Antora has raised $1 billion so far and is seeking a second assembly facility beyond its current factory in Silicon Valley.

Both companies are focused on making batteries out of cheap, domestically available materials that can store power at much lower cost than shorter-term lithium-based battery chemistries, and that also have little to no........

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