Shares in Ceres Power Holdings PLC (LSE:CWR, OTC:CPWHF) fizzled 42% lower to 75.75p after major partner Robert Bosch pulled its partnership as part of a strategic realignment of its operations.
The German giant will sell off its 17.44% stake and its non-executive board representative is stepping down with immediate effect.
Ceres noted that Bosch had issued a statement outlining plans to stop working on "stationary hydrogen technologies", meaning efforts in decentralised power-supply systems based on solid oxide fuel cells will come to an end, with its focus shifting to hydrogen electrolysis.
The market for solid-oxide fuel cells recently "has not developed as expected", Bosch said, with demands for higher-output systems with carbon capture, which "makes the conditions for economical operation significantly tougher".
The German company has informed Ceres that it will seek to end its partnership "in an orderly way, while continuing to meet its contractual obligations"
Ceres said its expectations were not changed for the current calendar year, with CEO Phil Caldwell saying: "Whilst Ceres is disappointed that Bosch will discontinue its operations relating to the industrialisation and preparation for production of decentralised power-supply systems using Ceres' solid oxide technology, we recognise that this decision is part of a broader revised strategic direction from Bosch and does not reflect its confidence around Ceres or our technology."
In a separate note, analysts at Panmure Liberum said: "Clearly, this is bad news and Bosch's intention to sell its stake will create a significant negative overhang on the shares."
The impact was more likely to be felt on the 2026 expectations, they added, with more detail likely to be shared at final results expected in March or April.