Amprius Technologies announced on May 21, 2025, 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. The uninterrupted flight, which concluded on April 28, 2025, at altitudes around 70,000 feet, surpassed Zephyr’s previous endurance record of 64 days. This marks the longest continuous aircraft flight ever recorded.
Amprius’s ultra-high-energy-density lithium-ion cells provided the critical energy storage necessary to keep the solar-powered Zephyr flying through multi-night cycles in the thin stratospheric air. These silicon anode batteries were instrumental in enabling reliable overnight power, a key factor in the mission’s success and continuous operation for over two months. Amprius's cells are among the only commercially available batteries capable of delivering the required endurance for persistent HAPS missions.
This achievement, building on a previous 64-day flight in 2022, underscores the reliability of Amprius’s technology and the Zephyr system’s ability to push aviation endurance limits. The record-breaking flight highlights the potential of HAPS platforms for commercial and defense applications such as continuous border surveillance, secure communications relay, and environmental monitoring, which require long-term, persistent coverage.
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