Form Energy's $750 million Series G backs 100-hour iron-air batteries

Form Energy, the Somerville, Massachusetts-based developer of iron-air batteries, said Thursday it raised $750 million in a Series G round led by T. Rowe Price. The company, founded in 2017, designs battery systems that can hold a charge for 100 hours—a bit more than four days—aimed at the long, still, cloudy stretches when wind and solar generation fade. The money will go toward expanding its Weirton, West Virginia, plant and paying for commercial deployments, the company said.

The Series G comes after a $405 million Series F in October 2024 and puts total equity raised above $2 billion. T. Rowe Price led that round too. New investors include Sequoia Capital, Janus Henderson, Franklin Templeton, and PEAK6 Investments. The returning group includes Prelude Ventures, Engine Ventures, TPG Rise Climate, Breakthrough Energy Ventures, Dustin Moskovitz and Cari Tuna, Coatue, Energy Impact Partners, GE Vernova, and M&G Catalyst Fund.

ESG Today first reported the financing.

Form Energy said the round comes after it signed commercial agreements with Xcel Energy, Google, Crusoe, and FuturEnergy Ireland. The company presents those agreements as evidence that multi-day storage is moving into the mainstream of grid planning, particularly for meeting rising electricity demand and coping with extreme weather. The batteries release stored power over days when renewables are quiet, giving grid operators a buffer through a long, calm, cloudy stretch.

For transition-finance desks, the round landed in a busy week. Copenhagen Infrastructure Partners closed a $3 billion growth markets fund, and Sonnedix signed a €730 million credit facility backed by nine banks. Those are diversified infrastructure vehicles. Form Energy's is a single-company bet, about a quarter of the CIP fund's size, aimed at proving one chemistry in one factory. The difference is between buying a market and buying a thesis. A $3 billion fund can absorb a project failure; a $750 million single-company round cannot.

The round arrives as the energy transition enters its most capital-hungry phase. Renewable generation has become cheap; the storage that makes it usable at all hours is now the cost barrier. Money is following that bottleneck, and a $750 million check for a manufacturing facility is a direct answer to the question of whether battery plants can scale as quickly as solar and wind farms.

This week also saw Citi revise its sustainable-finance framework to count data-center loans toward a $1 trillion green target, as this publication reported. The computing industry's appetite for power is one reason storage is in demand, and Form Energy's customers—a utility, a tech company, a digital-infrastructure firm, and an Irish energy developer—sit across that range.

The investor lineup has the look of a deliberate bridge between venture-stage climate finance and the public markets. Janus Henderson and Franklin Templeton, both managers of public-market money, are new names at this stage. Their presence suggests the cap table is being arranged with a future listing or a more liquid exit in mind. T. Rowe Price has now led two rounds in a row, and the second check is nearly twice the size of the first. That matters beyond the money. An institutional manager is willing to stay with the company through the hard part.

What remains is the manufacturing test. Weirton is where the iron-air battery becomes a product, and the company says the new money goes directly to that scale-up. The commercial agreements already signed give the factory a target. Whether Form Energy can produce those systems at a cost that declines as volumes rise will determine whether 100-hour storage becomes a standard grid asset or a proof of concept. The $750 million buys the chance to find out. If the chemistry works at volume, the round will look cheap; if not, it will look like a price for hope.