The startup storing the grid in a tank of pH-neutral water - no lithium, no fire, no drama.
Picture a shipping terminal on the Gulf Coast. Tanks, pipes, pumps - the unglamorous plumbing of industry. Tucked among them sits something that looks suspiciously ordinary: more tanks, more pipes, more pumps. Only this array is a battery. When it charges, nothing glows. When it discharges, nothing smokes. If a hose burst, what would spill out is closer to water than acid.
This is XL Batteries' first Organic Flow Battery, commissioned in 2025 in partnership with Stolthaven Terminals. It is deliberately boring, and that is the entire point. The company's wager is that the future of grid storage will not be won by the most exotic chemistry - it will be won by the one you can build from commodity parts and never have to evacuate the building for.
XL Batteries makes a flow battery: energy lives in a liquid, pumped through a cell that charges and discharges it. Where the industry standard dissolves vanadium in sulfuric acid, XL dissolves proprietary organic molecules in pH-neutral water. The result is non-flammable, non-toxic and non-corrosive - and, the company says, three to four times cheaper than the vanadium it replaces.
Want more hours of storage? Buy a bigger tank.
The XL Batteries design philosophyIn 2019, Tom Sisto was in a Columbia University lab synthesizing molecules for solar cells - specifically, a bright red pigment. His team noticed something strange: the molecule refused to degrade when it was charged and discharged, over and over. In most research that would be a curiosity. Sisto saw a battery.
A molecule that never wears out is exactly what a storage system needs. XL Batteries was founded to commercialize that patented chemistry, and Sisto - now CEO - recruited a team with unusually deep battery pedigree, including a co-founder and CTO of A123 Systems (the largest battery IPO of 2009) plus executives from Pfizer and Plug Power.
The mission is plainly stated: create the world's lowest-cost, safest and most efficient long-duration energy storage. The subtext is geopolitical. XL's feedstocks are abundant and domestically sourced - a deliberate hedge against China's grip on the lithium supply chain.
Proprietary organic molecules derived from abundant oil-and-gas feedstocks, dissolved in pH-neutral water. No vanadium, no sulfuric acid, no corrosion.
Built from commercially available pumps, tubes and tanks - not exotic supply chains. If you can plumb it, you can scale it.
Power and energy are decoupled. Need 10, 20 or 50 hours of discharge? Enlarge the tanks. Storage becomes a plumbing decision, not a chemistry problem.
Non-flammable, non-toxic, non-corrosive. A leak is a spill, not a hazmat event - which changes where and how you can site it.
By late 2025, XL Batteries had raised roughly $28 million in total capital across seed financing, backed by climate and strategic investors.
Commissioned its first Organic Flow Battery in a live pilot with Stolthaven Terminals - the debut deployment of XL's long-duration technology.
Partnered with Prometheus Hyperscale to deploy long-duration storage at U.S. data centers, smoothing the ravenous, spiky loads of AI compute.
Raised $7.5M from Merrin Investors, the family office of entrepreneur Seth Merrin, bringing total capital to roughly $28M.
XL sells to the parts of the economy that need a lot of power for a long time and can't afford a fire: utilities and grid operators smoothing renewables, industrial and chemical terminals hardening their own supply, and - increasingly - the data-center developers scrambling to feed AI.
The pitch to each is the same. Renewables are cheap but intermittent; the grid needs somewhere to park energy for hours or days at a stretch. Lithium-ion is superb for short bursts and pricey for long hauls. XL's flow battery is built for exactly the long hauls lithium struggles with - and it can sit next to a building without a sprinkler-system argument.
The core molecule started life as bright red paint for solar cells. It simply refused to degrade - so they made it a battery.
Run time is set by tank size. Storage capacity becomes a question for the plumbing department.
The electrolyte is pH-neutral water. Worst case looks more like a mop job than an evacuation.
Pumps, tubes and tanks you can buy today - no bespoke supply chain to hold the whole thing hostage.
Return to that Gulf Coast terminal. The array is still there, still humming, still refusing to be interesting. But the meaning of the scene has shifted. What looked like ordinary plumbing has quietly become an argument - that the grid can be backed by storage nobody has to fear, built from parts nobody has to import, running for decades on a molecule that was almost thrown away.
Six years ago it was a red pigment on a Columbia lab bench. Now it is on a factory floor in Marlborough and a terminal in Texas, and soon, if the data-center deals hold, humming beside the servers training the next model. XL Batteries hasn't won the grid yet. But it has made the boring battery worth watching - and in energy, boring is a compliment.
How a degradation-proof molecule from a Columbia solar lab turned into a storage company.
What it took to commission XL's first Organic Flow Battery at Stolthaven's terminal.
The case for non-flammable, commodity-built flow batteries.
The flow architecture that decouples power from energy capacity.
How the Prometheus Hyperscale deal aims flow batteries at compute-hungry loads.
Domestic feedstock as a geopolitical hedge for a Marlborough startup.