Somewhere between 720 megawatts and 2 gigawatts of battery capacity now sits behind the meter at SpaceXAI's Colossus 2 data center in Memphis — and nobody with official knowledge will confirm the exact figure.

Canary Media counted 720 Tesla Megapack containers in satellite imagery of the Southaven site dated July 11. Depending on which Megapack model is installed, that equates to 2.8 gigawatt-hours and between 720 MW and 1,400 MW of discharge capacity. For scale, the largest known grid battery operating in the U.S. today is the Edwards & Sanborn installation in Kern County, California, at more than 1,066 MW and 3,287 MWh.

The company itself claims more. On Aug. 20, SpaceXAI energy and data center developer Riley Trettel told the board of the Tennessee Valley Authority — the federal utility serving 10 million people across the Southeast — that the facility holds 3.3 GWh of storage, "enough to power all of Memphis for two hours." The battery was not yet connected to TVA's grid, Trettel said, but could be later this year if the board approved. The board approved a direct hookup that same day.

Doug McGowan, CEO of Memphis Light, Gas and Water, the municipal utility serving the facility, corroborated the scale on Sept. 2 at a solar and storage conference in Chattanooga. "It's the world's largest supercomputer today, but it's also got the world's largest grid-connected battery system," McGowan said. "I think it's 2,000 MW of batteries behind the meter that they have to help as a backup when they have to curtail."

MLGW's communications team declined to clarify the size and referred questions to TVA and SpaceXAI. TVA declined to comment. SpaceXAI has not responded to requests for comment.

The procurement trail is documented. xAI bought $430 million worth of Megapacks last year, Tesla disclosed in a January SEC filing. After SpaceX acquired xAI in February, the combined company bought another $405 million worth in the first half of this year. Tesla began production of a redesigned, faster-to-deploy Megapack 3 at its Texas factory in early August — after the satellite imagery was taken — meaning installed capacity at Colossus 2 may have grown further.

No contract, no permits, no precedent

The build breaks the standard development model. Grid-scale storage projects typically take years, moving through community outreach for permits and a utility-led contracting process to guarantee revenue. SpaceXAI built anyway, with no announced utility contract. Regional storage industry leaders learned of the battery at the August TVA board meeting.

The company has already run Colossus 2 on a fleet of mobile gas generators without air permits, claiming an exemption because the units are mobile. Sixty-nine generators were active as of July, running day after day in the same location and emitting pollutants that affect nearby predominantly Black neighborhoods including Whitehaven and Boxtown. The Southern Environmental Law Center has sued to stop the unpermitted pollution; the case remains pending. The battery could reduce generator use — or, in an islanded microgrid setup, charge from them.

The interruption bargain

The battery operates under a "power interruption" program run by MLGW, McGowan said. "They actually have behind-the-meter generation and storage that can meet all of their load, so that they can actually successfully come off the grid for four hours in order to curtail, so that nobody else has to," he said. That capability was a precondition for connecting the data center. "We kind of proved the model here before the ratepayer protection plan was in place," McGowan added, referring to the White House-led pact urging AI companies to fund their own infrastructure.

The approach mirrors deals elsewhere. Aligned Data Centers will come online in Oregon years early by paying the utility to build peak-capacity batteries. Google signed a portfolio of solar, wind and batteries for a Minnesota data center.

For TVA, the asset may become a contracted grid resource. The utility identified storage as a growth opportunity in its long-range energy plan, approved by the board in August, and signed its own contract with Plus Power in April for a 200-MW/800-MWh battery in Jackson County, Alabama, due in 2029. "We're just beginning to tap the potential of battery storage in the Tennessee Valley," said Gil Hough, executive director of the Tennessee Solar Energy Industries Association. "A project this large shows what's possible — and it could be a real catalyst for utilities, solar developers, and other energy companies to think much bigger."

The next milestone is the grid connection itself: whether TVA signs a contract turning the privately built Memphis battery into a paid peak-capacity resource — and whether the pending SELC lawsuit forces the generator fleet offline first.