Waratah Super Battery Reaches Full 850 MW After Transformer Failure

On 28 September 2026, the Waratah Super Battery cleared the threshold its owners had been working toward for more than a year: full 850 MW output, approved and operational, after a transformer failure had held the project below its rated ceiling since late 2025.

The scale here is worth stating plainly. This is Australia’s largest grid-scale storage facility, and it holds the country’s biggest contracted system-security obligation. Its return to full rated power matters to the operators managing Sydney’s transmission constraints and to anyone tracking how quickly utility-scale batteries actually reach their design capability in the real world.

According to a report by Veselina Petrova via Renewables Now on 28 September 2026, the milestone followed transformer replacement and testing completed earlier in the month, with Australian Energy Market Operator (AEMO) approval received around the same date.

Here is what the milestone covers, what it does not, and why the distinction matters for anyone tracking grid-scale storage in Australia.

What the 850 MW milestone actually means

The technical threshold crossed on 28 September 2026 was power output: the battery can now discharge at its full rated 850 MW. That number matters because of what came before it.

Since at least February 2025, the battery had been running at 700 MW, or 82% of its rated power. An Akaysha Energy statement dated 21 February 2025 and a later Energy-Storage.news report on 5 June 2026 both confirmed the same sustained operating state: 700 MW of power, but 1,680 MWh of energy already at full rated level.

That last detail is the one most capacity announcements blur. Power rating (how hard the battery can push, measured in MW) and energy capacity (how much it can store, measured in MWh) are two different dimensions. The energy side, 1,680 MWh, was never the problem. It had been operational throughout the constrained period. What changed in September 2026 was the power side finally reaching its ceiling.

Battery performance parameters, particularly the relationship between power rating (MW) and energy capacity (MWh), are frequently conflated in project announcements; the distinction is what made Waratah’s constrained period technically significant, given that its energy capacity remained fully operational throughout while only its power ceiling was affected.

850 MW was reached in a brief test on 7 September 2026, the first time the full rated output had been achieved since the catastrophic failure of High Voltage Transformer 3.

For investors reading capacity figures, the three milestones are worth keeping separate:

• Sustained 700 MW operation from at least February 2025, with full 1,680 MWh energy capacity already confirmed
• First 850 MW test output reached 7 September 2026
• Full 850 MW / 1,680 MWh capacity milestone confirmed around 28 September 2026, following AEMO approval

The gap between 700 MW and 850 MW is not a rounding difference. It is the difference between a project meeting its contracted minimum and a project delivering its full design capability. When you read that a battery is at “full capacity,” it is worth checking which of those two things the writer actually means.

How a transformer failure delayed full commissioning by nearly a year

The reason the milestone took over a year to reach comes down to a single component. In October 2025, with the project on the verge of full commissioning, High Voltage Transformer 3 suffered what Energy-Storage.news later described, in its 10 September 2026 report, as a catastrophic failure.

RenewEconomy reported on 14 November 2025 that the failure pushed expected full operation back into 2026 and triggered further reductions, or “haircuts,” to Akaysha’s expected revenues under its grid-security contract.

That revenue mechanism is the part investors should sit with. Payment under the System Integrity Protection Scheme (SIPS) is tied to the service actually delivered, not to nominal installed capacity. So when the battery could not reach its contracted output, the contracted income shrank alongside it.

The recovery arc

Getting back to full power was a staged process. The sequence ran as follows:

1. High Voltage Transformer 3 failed in October 2025, on the verge of full commissioning
2. The battery continued operating at a constrained 700 MW through mid-2026
3. Recovery testing reached 850 MW on 7 September 2026, the first full-output test since the failure
4. A SIPS-consistent discharge test of 701 MW was conducted on 9 September 2026
5. Full 850 MW / 1,680 MWh capacity was confirmed by late September 2026

For anyone evaluating large-scale battery projects, this is a concrete lesson in performance risk. A single transformer simultaneously constrained contracted revenue, delayed commissioning milestones, and raised questions about grid-security delivery during the gap. Under a 5.5-year SIPS contract signed in 2022, where payment follows delivered service rather than installed hardware, that kind of setback lands directly on the income statement. The milestone reads as earned, not routine.

The SIPS contract and why Transgrid needed this battery at full power

Shift the lens from Akaysha’s story to the grid operator’s, and the reason the missing 150 MW mattered comes into focus. Transgrid does not treat this battery as a market participant it happens to buy from. It treats it as command-activated infrastructure.

Under the SIPS arrangement, Transgrid monitors the network for disturbances such as lightning strikes or extreme weather. When one hits, it can call the battery to inject energy while simultaneously instructing paired generators to adjust output. Energy-Storage.news, in a 23 January 2025 analysis, described the effect as a “giant shock absorber” for the Sydney grid. The battery creates dynamic headroom on the transmission network, allowing more power to flow into Sydney without new lines being built first.

A Wood Mackenzie-hosted article from 28 August 2025 quoted Phil Bratby, EnergyCo executive project director, on how the mechanism works.

The SIPS enables Transgrid to send control signals to the battery while instructing paired generators to ramp, enhancing system resilience and demonstrating a new operational model in which batteries actively support system strength, said Phil Bratby, EnergyCo executive project director.

The contracted obligation and the installed capacity are deliberately different. The Australian Energy Regulator (AER) determination of 17 October 2022 records a guaranteed minimum of 700 MW continuous power and 1,400 MWh usable energy. The installed system sits above that at 850 MW / 1,680 MWh, giving deliberate headroom over the contracted floor.

The enabling spend tells its own story. Transgrid committed $150 million to transmission upgrades and $30 million to the SIPS control system, a total of $180 million in network co-investment sitting alongside Akaysha’s undisclosed project cost. That signals something important for investors: grid-scale battery integration at this level requires network co-investment of a scale that shapes where and when such projects are even viable. Wood Mackenzie characterises the resulting SIPS contract as the largest of its kind in Australia.

This is what separates Waratah from a conventional merchant battery play. Part of it operates as regulated grid infrastructure, part as a market participant, a hybrid model with different risk and return characteristics than either approach alone.

Grid-scale energy storage projects in Australia operate across a spectrum from pure merchant assets to regulated infrastructure, and Waratah’s hybrid positioning, part SIPS-contracted, part NEM market participant, reflects a structural evolution in how large batteries are designed to earn revenue.

From Munmorah coal station to grid-forming storage: what this site represents

The location closes the loop on the story. The battery sits on the site of the former Munmorah coal-fired power station near Budgewoi, New South Wales. Australia’s largest grid-scale battery now stands where a coal plant used to burn, a fossil-fuel-to-storage transition on the same footprint.

What distinguishes this project from earlier Australian batteries is not scale alone. The Hornsdale Power Reserve in South Australia and the Victorian Big Battery in Victoria built their reputations on regional stability, frequency control, and market arbitrage. Waratah operates on a different footing:

• Deep transmission integration, with Transgrid able to command the battery directly in concert with paired generators through SIPS
• An explicit Sydney Ring mandate, positioning it as core grid equipment rather than a merchant generation asset
• The largest contracted system-security obligation of any battery in Australia

Wood Mackenzie framed this operational model, in its 28 August 2025 article, as a step change. Rather than functioning as an arbitrage asset that buys low and sells high, Waratah behaves more like core grid infrastructure, and Wood Mackenzie places it within a group of projects positioning Australia as a leading country for grid-forming battery energy storage technology.

For investors tracking the energy transition across the Asia-Pacific region, the Munmorah shift from coal to storage on a single site is a tangible illustration of an asset-class change underway. Decommissioned fossil-fuel sites are becoming candidates for utility-scale storage rather than simple remediation and closure.

Battery storage capacity growth globally is accelerating fastest in markets where grid planners have shifted from treating storage as supplementary peaking capacity to integrating it as core transmission infrastructure, a transition Waratah now exemplifies at the project level.

The read for you is structural. When grid planners treat storage as transmission infrastructure rather than supplementary capacity, it reshapes the contracts, revenue certainty, and co-investment structures that large-scale projects can attract. That is the shift Waratah embodies, and it changes how the next generation of projects will likely be financed in Australia.

What full capacity changes, and what the gaps still tell you

The milestone answers one question cleanly. Whether Waratah could recover from the transformer failure and deliver its full rated capability is no longer open. As of late September 2026, it can discharge at 850 MW with 1,680 MWh behind it, and AEMO has signed off.

What full capacity does not resolve is the economics. Three data gaps remain material for anyone trying to benchmark this project:

• No consolidated project capital cost has been publicly disclosed
• No SIPS service revenue figure has been made public
• The merchant portion of capacity, roughly 350 MW, remains exposed to volatile National Electricity Market (NEM) spot and ancillary services markets

The absence of a disclosed capital cost and revenue figure means you cannot calculate a return on this project from public data alone. That is a real limitation if you are trying to compare Australia’s grid-scale storage economics against other markets. Knowing what is not yet knowable is as useful as knowing what is confirmed.

The regulatory risks embedded in a contract like SIPS extend beyond the contracted power floor: changes to market rules, ancillary service definitions, or AER network determination criteria can all reshape the revenue certainty that makes infrastructure-grade battery contracts attractive to long-term capital.

For the forward watch, keep two things in view. The SIPS contract runs 5.5 years from 2022, setting a regulatory horizon to track, and one named infrastructure event will eventually change Waratah’s role.

The Hunter Transmission Project is the named successor that will eventually reduce Waratah’s bridging role, taking over the transmission-support function the battery now provides during New South Wales’s exit from coal generation.

This article is for informational purposes only and should not be considered financial advice. Investors should conduct their own research and consult with financial professionals before making investment decisions.