Exhibit 16.2

December 9, 2021

Securities and Exchange Commission

100 F Street, N.E.

Washington, DC 20549

Commissioners:

We have read the statements made by ESS Tech, Inc. (formerly ACON S2 Acquisition Corp.) regarding our Firm’s dismissal included on pages 81 and 82 of the Post-Effective Amendment No. 1 to Form S-1 dated December 9, 2021. We agree with the statements concerning our Firm’s dismissal in such Post-Effective Amendment No. 1 to Form S-1.

Very truly yours

Marcum LLP

PM/mm

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