ESS Tech, Inc.

REPORT OF KPMG LLP

INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the Stockholders and the Board of Directors

ESS Tech, Inc.:

Opinion on the Consolidated Financial Statements

We have audited the accompanying consolidated balance sheets of ESS Tech, Inc. (the Company) as of December 31, 2025 and 2024, the related consolidated statements of operations and comprehensive loss, stockholders’ equity, and cash flows for each of the years in the two-year period ended December 31, 2025, and the related notes (collectively, the consolidated financial statements). In our opinion, the consolidated financial statements present fairly, in all material respects, the financial position of the Company as of December 31, 2025 and 2024, and the results of its operations and its cash flows for each of the years in the two-year period ended December 31, 2025, in conformity with U.S. generally accepted accounting principles.

Going Concern

The accompanying consolidated financial statements have been prepared assuming that the Company will continue as a going concern. As discussed in Note 1 to the consolidated financial statements, the Company has recurring net losses from operations and is generating negative cash flows from operating activities which raise substantial doubt about its ability to continue as a going concern. Management’s plans in regard to these matters are also described in Note 1. The consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty.

Basis for Opinion

These consolidated financial statements are the responsibility of the Company’s management. Our responsibility is to express an opinion on these consolidated financial statements based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) (PCAOB) and are required to be independent with respect to the Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the consolidated financial statements are free of material misstatement, whether due to error or fraud. The Company is not required to have, nor were we engaged to perform, an audit of its internal control over financial reporting. As part of our audits, we are required to obtain an understanding of internal control over financial reporting but not for the purpose of expressing an opinion on the effectiveness of the Company’s internal control over financial reporting. Accordingly, we express no such opinion.

Our audits included performing procedures to assess the risks of material misstatement of the consolidated financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the consolidated financial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the consolidated financial statements. We believe that our audits provide a reasonable basis for our opinion.

Critical Audit Matter

The critical audit matter communicated below is a matter arising from the current period audit of the consolidated financial statements that was communicated or required to be communicated to the audit committee and that: (1) relates to accounts or disclosures that are material to the consolidated financial statements and (2) involved our especially challenging, subjective, or complex judgments. The communication of a critical audit matter does not alter in any way our opinion on the consolidated financial statements, taken as a whole, and we are not, by communicating the critical audit matter below, providing a separate opinion on the critical audit matter or on the accounts or disclosures to which it relates.

Liquidity and Going Concern

As discussed in Note 1 to the consolidated financial statements, the Company has incurred operating losses and cash outflows from operations since inception, and the Company anticipates that losses will continue in the near term. During the year ended December 31, 2025, the Company incurred net losses of $63.4 million and used $50.3 million of cash in operating activities. As of December 31, 2025, the Company had unrestricted cash and cash equivalents of $14.5 million and short-term investments of $7.5 million. The continuation of the Company as a going concern is dependent upon its ability to obtain additional debt or equity financing and to generate profit from its operations. Any

• 58 - such financing activities are subject to market conditions and accordingly involve factors that are outside the Company’s control. These uncertainties cause substantial doubt to exist as to the Company’s ability to continue as a going concern for 12 months from the issuance of the financial statements.

We identified the evaluation of the Company's ability to continue as a going concern and related disclosures as a critical audit matter. A high degree of subjective auditor judgment and increased audit effort was required to evaluate the Company’s going concern analysis and the adequacy of the financial statement disclosures related to the going concern assessment.

The following are the primary procedures we performed to address this critical audit matter. We obtained the Company’s going concern analysis and evaluated whether the analysis and conclusions reached comply with relevant accounting literature. We assessed the conditions and events that raise substantial doubt about the Company’s ability to continue as a going concern. We inquired of executive officers and key members of management of the Company regarding factors that would have an impact on the Company’s ability to continue as a going concern, including the need for additional financing given the Company’s projected monthly cash outflows. We obtained and read the agreements related to the Company’s outstanding financing obligations, including subsequent events. We assessed the Company’s disclosures related to its going concern assessment by comparing the disclosures to the audit evidence obtained.

/s/KPMG LLP

We have served as the Company’s auditor since 2023.

Portland, Oregon

March 5, 2026

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