Grid batteries are usually announced once and then talked about as if nothing changed. Eraring’s has changed three times since its first stage was committed, and each change is documented in Origin’s own releases, so the growth can be laid out exactly. This is Origin’s table from its 11 December announcement of the fourth stage, condensed for width; figures and dates are as Origin published them:
| Stage | Announced | Est. commercial operation | Outcome, per Origin’s table |
|---|---|---|---|
| Stage 1 | Apr 2023 | End-2025 | 460 MW at roughly two hours’ dispatch (1,070 MWh) |
| Stage 2 | Jul 2024 | Q1 2027 | Additional 240 MW, grid-forming, 4.3 hours (1,030 MWh) |
| Stage 3 | Nov 2024 | End-2025 | Adds 700 MWh to Stage 1, extending it to 460 MW / four hours (1,770 MWh) |
| Stage 4 | Dec 2025 | Q1 2027 | Adds 360 MWh to Stage 2, extending it to 240 MW / 5.8 hours (1,390 MWh) |
Bars run from Origin’s announcement date to its estimated commercial operation date, as stated in the 11 December 2025 release. Solid bars are complete; outlined bars are under construction. “End-2025” and “Q1 2027” are drawn as December 2025 and March 2027.
Two batteries, four stages
On its project page, Origin now folds the four stages into two plain-English objects. “Battery 1” is stages 1 and 3 together: 460 MW with 1,770 MWh of storage, four hours’ dispatch, which the page says “is now complete and operating in the National Electricity Market.” “Battery 2” is stages 2 and 4: another 240 MW with about 1,390 MWh, running to 5.8 hours, under construction and described as on track for the first quarter of 2027. The page records the practical texture of a live site: Origin has approval for extended construction hours, Saturday afternoons and Sundays, through to 31 December 2026, to get energisation, testing and commissioning done.
Battery 2 also carries a technical term worth one plain sentence. A “grid-forming” battery does not just push energy into a live grid; its inverters can help set the grid’s voltage and frequency rhythm the way heavy spinning generators do, which is part of the system-strength service coal units currently provide. On the same site as four of those coal units, that is not an accidental specification.
The pattern: the megawatts stayed, the hours deepened
Look down the table’s outcome column and one pattern carries the story. The project’s power rating has been 700 MW since the original development assessment in 2022; every subsequent decision spent money on duration instead. Stage 3 stretched Battery 1 from two hours to four; Stage 4 stretches Battery 2 from 4.3 hours to 5.8. Origin’s December release put the total at 3,160 MWh, against the 2,800 MWh first assessed, and committed $80 million to the fourth stage, with equipment from the Finnish group Wärtsilä and construction by Enerven. In the December release Origin’s then head of energy supply and operations, Greg Jarvis, called the site “the largest approved battery energy storage system in the Southern Hemisphere.”
Duration is the quiet race in the whole market. A two-hour battery shifts the evening peak; a five-to-six-hour battery starts covering the shoulder of a whole evening, which is the work a retiring coal unit leaves behind. AEMO’s latest Quarterly Energy Dynamics report measured NEM-wide battery discharge averaging 359 MW in the first quarter of 2026, more than three times the level a year earlier, with grid-scale battery capacity passing 8,000 MW after 4,445 MW was commissioned in twelve months. Eraring’s build is the Hunter’s share of that national surge, and on Origin’s site transition page it carries a longer meaning: the company calls the battery “the first step in the transition of the Eraring site” ahead of the coal units’ scheduled April 2029 closure.
One attribution note. Origin’s December quotes are from Greg Jarvis in his role at the time; Origin has since named Andrew Thornton to lead energy supply and operations. The figures above are as published and remain on Origin’s live pages, which we re-read on 18 July 2026.