Acquisition Expands ESS Technology Portfolio and Strengthens Path to Lower-Cost, Scalable Long-Duration Storage

Key VoltStorage Executive and Engineering Personnel Join ESS, Strengthening the Commercial and Technical Bench

ESS Tech, Inc. (“ESS” or the “Company”), a leading innovator in long-duration energy storage solutions, today announced the acquisition of the intellectual property and assets of VoltStorage GmbH, a pioneer in iron-salt battery technology. This strategic move combines two complementary technologies to deliver the most flexible, cost-effective long-duration energy storage solution available on the market. The combined platform will set a new industry standard for performance, sustainability, and affordability. This acquisition adds VoltStorage’s portfolio of patents and technical development work to ESS’ robust existing intellectual property base. Through the transaction, ESS also gains access to skilled personnel with deep electrochemistry, materials science, and technology development background.

ESS believes the combined capabilities will accelerate strategic growth, expand market reach, and position the company at the forefront of long-duration energy storage solutions.

The resulting solution will enable utilities, renewable developers, and industrial customers to discharge energy over extended durations to improve grid reliability and increase the usable value of intermittent renewable generation, delivering the industry’s lowest Levelized Cost of Energy (LCOE).

Key Benefits of the Combined Technology:

• Flexibility: Potential to address a wider range of diverse applications, from grid-scale storage to industrial microgrids.
• Lowest Cost Long-Duration Storage: Leveraging abundant, sustainable materials to deliver superior economics.
• Sustainability and Scale: Iron-based chemistry ensures environmental responsibility and operational safety.
• Enhanced U.S. Manufacturing Platform: Deploys international development expertise at ESS’ American manufacturing facility

“This acquisition accelerates our mission to provide clean, reliable, and affordable energy storage solutions worldwide,” said Drew Buckley, CEO of ESS. “By combining decades of iron flow battery expertise across two companies at ESS, we are accelerating innovation to create the most advanced iron-salt battery platform for long-duration storage.”

About ESS Tech, Inc.

ESS (NYSE: GWH) is the leading manufacturer of long-duration iron flow energy storage solutions. ESS was established in 2011 with a mission to accelerate decarbonization safely and sustainably through longer lasting energy storage. Using easy-to-source iron, salt, and water, ESS iron flow technology enables energy security, reliability and resilience. We build flexible storage solutions that allow our customers to meet increasing energy demand without power disruptions and maximize the value potential of excess energy. For more information visit www.essinc.com.

Forward-Looking Statements

This communication contains certain forward-looking statements, including statements regarding ESS and its management team’s expectations, hopes, beliefs, intentions or strategies regarding the future. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intends,” “may,” “might,” “plan,” “possible,” “potential,” “predict,” “project,” “should,” “will,” “would” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that a statement is not forward-looking. Examples of forward-looking statements include, among others, statements regarding the expected integration of the VoltStorage intellectual property and technology, ESS product development and manufacturing, and relationships with customers. These forward-looking statements are based on ESS’ current expectations and beliefs concerning future developments and their potential effects on ESS. Many factors could cause actual future events to differ materially from the forward-looking statements in this communication. There can be no assurance that the future developments affecting ESS will be those that we have anticipated. These forward-looking statements involve a number of risks, uncertainties (some of which are beyond ESS control) or other assumptions that may cause actual results or performance to be materially different from those expressed or implied by these forward-looking statements, which include, but are not limited to, general economic and market conditions as well as geopolitical developments and other risks and uncertainties described more fully in the section titled “Risk Factors” in the Company’s Quarterly Report on Form 10-Q filed on November 13, 2025, and the Company’s other filings with the U.S. Securities and Exchange Commission. Except as required by law, ESS is not undertaking any obligation to update or revise any forward-looking statements whether as a result of new information, future events or otherwise.

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