05:23 AM EDT, 10/10/2025 (MT Newswires) -- ESS Tech ( GWH/WS ) shares were up nearly 26% in recent premarket activity Friday after the company disclosed a new iron flow battery pilot to deliver power under a 10-year agreement with Salt River Project, a not-for-profit public power utility serving the greater Phoenix metropolitan area.

The agreement involves adding a 5-megawatt, 50 megawatt-hour battery system to the grid, the parties said late Thursday.

The Iron Flow Battery project aims to evaluate the performance of non-lithium, long-duration energy storage in the Arizona climate. The pilot seeks to validate the company's technology as a safer and sustainable alternative to lithium-ion batteries, it said.