AALTO Zephyr Achieves World-Record 67-Day Flight Powered by Amprius Ultra-High-Energy Batteries

Record Stratospheric Flight Highlights Operational Value of Amprius' High-Performance Batteries for HAPS Platforms

Amprius Technologies, Inc. ("Amprius" or the "Company") (NYSE:AMPX), a leader in next-generation lithium-ion battery technology, today announced that its silicon anode batteries powered AALTO's Zephyr high-altitude pseudo-satellite (HAPS) aircraft during a world-record-setting 67-day flight in the stratosphere, which concluded on April 28, 2025. This uninterrupted flight, conducted at altitudes around 70,000 feet, surpassed Zephyr's previous endurance record of 64 days and marks the longest continuous aircraft flight ever recorded.

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AALTO Zephyr Achieves World-Record 67-Day Flight Powered by Amprius Ultra-High-Energy Batteries

The Zephyr is a solar-powered unmanned aerial vehicle that operates in the stratosphere, charging its batteries during the day via solar panels and relying on battery power overnight. Amprius' ultra-high-energy-density lithium-ion cells provided the critical energy storage needed to keep the Zephyr flying through multi-night cycles in the thin air of the stratosphere. By enabling reliable overnight power, these silicon anode batteries were a key factor in the mission's success, allowing the aircraft to maintain continuous operation for over two months. Amprius' cells are among the only commercially available batteries known that are capable of delivering the required endurance for persistent HAPS missions, a capability that was essential for Zephyr's day-and-night flight longevity.

This achievement was made possible through the close collaboration between Amprius and AALTO HAPS ("AALTO"), a U.K.-based Airbus subsidiary that designs, manufactures, and operates Zephyr. Amprius has been a key supplier of high-performance batteries to AALTO for several years, including for a 2022 Zephyr flight that lasted 64 days. The new 67-day flight builds on that milestone, further proving the reliability of Amprius' technology and the Zephyr system's ability to push the limits of aviation endurance.

"We are extremely proud to see our batteries enable this groundbreaking 67-day flight," said Dr. Kang Sun, CEO of Amprius Technologies. "This accomplishment demonstrates the transformative impact of our silicon anode battery technology in aerospace. By providing the energy needed to keep Zephyr flying through the night, our silicon anode cells made it possible to achieve a new level of endurance for stratospheric aircraft. We are honored to partner with AALTO in pushing the boundaries of what high-altitude platforms can do for both commercial and defense applications."

"Achieving this 67-day flight is a major milestone for Zephyr and HAPS technology more widely," said Pierre-Antoine Aubourg, Chief Technical Officer at AALTO. "Amprius' high-energy batteries provided the reliable power storage we needed to maintain Zephyr's day and night operations. Their technology was instrumental in enabling us to break our own endurance record, demonstrating that persistent stratospheric missions and capabilities are now a reality. We look forward to continuing our collaboration with Amprius as we focus on our remaining flight program for 2025."

The record-breaking flight underscores the potential of high-altitude pseudo-satellite platforms for both commercial and defense applications. Operating at roughly 70,000 feet, the Zephyr can fly for months at a time, effectively combining the persistence of a satellite with the flexibility of an unmanned aerial vehicle. This capability opens the door for missions such as continuous border surveillance, secure communications relay, and environmental monitoring that require long-term, persistent coverage. Such ultra-long endurance is especially valuable for defense, where HAPS vehicles like Zephyr can provide persistent ISR (intelligence, surveillance, and reconnaissance) and connectivity over critical areas without interruption.

For more information, please visit the Amprius investor relations website at ir.amprius.com.

About Amprius Technologies, Inc.

Amprius Technologies, Inc. is a leading manufacturer of high-energy and high-power lithium-ion batteries, producing the industry's highest-known energy density cells. The Company's commercially available SiMaxx™ batteries deliver up to 450 Wh/kg and 1,150 Wh/L, with third-party validation of 500Wh/kg and 1,300 Wh/L. Amprius expanded its product portfolio to include the SiCore® platform in 2024, significantly enhancing its ability to serve additional customer applications. The Company's corporate headquarters is in Fremont, California, where it maintains an R&D lab and a MWh scale manufacturing facility for the fabrication of silicon anodes and cells. To serve customer demand, Amprius entered into several agreements to secure over 1.8GWh of contract manufacturing capacity available today. For additional information, please visit amprius.com. Also, see the Company's LinkedIn and Twitter pages.

About AALTO

Based in Farnborough, UK, AALTO is an Airbus subsidiary that designs, manufactures and operates the Zephyr High Altitude Platform Station (HAPS). Powered by solar energy and operating above 60,000+ feet, Zephyr's persistence enables continuous flight for months at a time. Its flight-time record is over 67 days in the stratosphere: a world-record for global aviation. As a payload agnostic platform, Zephyr can deliver several applications including targeted surveillance, disaster management, border protection, and precision agriculture. To find out more about AALTO and the Zephyr High Altitude Platform Station, visit aaltohaps.com.

Forward-Looking Statements

This press release includes "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934, each as amended. Forward-looking statements may be identified by the use of words such as "estimate," "plan," "project," "forecast," "intend," "expect," "anticipate," "believe," "seek," "will" or other similar expressions that predict or indicate future events or trends or that are not statements of historical matters. These forward-looking statements include, but are not limited to, statements regarding the impact of silicon anode technology in aerospace, the performance of Amprius' products, the benefits of Amprius' products to both commercial and defense applications, the collaborative relationship of Amprius with AALTO, and the potential applications of AALTO's products. These statements are based on various assumptions, whether or not identified in this press release, and on the current expectations of Amprius' management and are not predictions of actual performance. Actual results could differ materially from these forward-looking statements as a result of certain risks and uncertainties. These forward-looking statements are subject to a number of risks and uncertainties, including risks related to the ability of Amprius to continue developing and manufacturing high-performing batteries for HAPS applications; Amprius' liquidity position; risks related to the rollout of Amprius' business and the timing of expected business milestones; the effects of competition on Amprius' business; supply shortages in the materials necessary for the production of Amprius' products; and changes in domestic and foreign business, market, financial, political and legal conditions. For more information on these risks and uncertainties that may impact the operations and projections discussed herein can be found in the documents we filed from time to time with the Securities and Exchange Commission (the "SEC"), all of which are available on the SEC's website at www.sec.gov. There may be additional risks that Amprius does not presently know or that Amprius currently believes are immaterial that could also cause actual results to differ from those contained in the forward-looking statements. In addition, forward-looking statements reflect Amprius' expectations, plans or forecasts of future events and views as of the date of this press release. These forward-looking statements should not be relied upon as representing Amprius' assessments as of any date subsequent to the date of this press release. Accordingly, undue reliance should not be placed upon the forward-looking statements. Except as required by law, Amprius specifically disclaims any obligation to update any forward-looking statements.

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