ESS Tech, Inc. Announces Successful Update to Historical SPAC (Acon S2 Acquisition Corp.) Financials

Pre-Merger ACON STWO financials now updated for regulatory compliance

WILSONVILLE, Ore.–(BUSINESS WIRE)–ESS Tech, Inc. (“ESS” or the “Company”) (NYSE:GWH), a U.S. manufacturer of long-duration batteries for utility-scale and commercial energy storage applications, announced today that it has successfully completed the restatement of the legacy financial filings from Acon S2 Acquisition Corp. (“ACON”) to ensure compliance with regulatory requirements.

“The restatements required addressing certain accounting standards, specifically the reclassification of Class A shares from equity to mezzanine equity, on legacy ACON financials. Because this issue pre-dated our merger closing with ACON, the restatement had no impact on ESS’ operating company, its current operations or financial statements,” said Amir Moftakhar, CFO of ESS. “I am pleased we were able to complete and file these so quickly and am thankful for the support of ACON’s auditors in resolving this so efficiently.”

About ESS Tech, Inc.

ESS (NYSE: GWH) designs, builds and deploys environmentally sustainable, low-cost, iron flow batteries for long-duration commercial and utility-scale energy storage applications requiring from 4 to 12 hours of flexible energy capacity. The Energy Warehouse™ and Energy Center™ use earth-abundant iron, salt, and water for the electrolyte, resulting in an environmentally benign, long-life energy storage solution for the world’s renewable energy infrastructure. Established in 2011, ESS enables project developers, utilities, and commercial and industrial facility owners to make the transition to more flexible non-lithium-ion storage that is better suited for the grid and the environment. For more information, visit www.essinc.com.

Contacts

Investors:

Erik Bylin

investors@essinc.com

Media:

Gene Hunt

Trevi Communications, Inc.

978-750-0333 x.101

gene@trevicomm.com