AALTO tests Amprius SiCore batteries on Zephyr flights above 20 km
AALTO is testing Amprius SiCore battery cells on its Zephyr aircraft in the stratosphere, a key step for ultra-long-endurance UAV operations. The trial puts a new high-energy cell into one of the most demanding use cases in aviation: keeping a solar-powered aircraft flying through the night at altitudes above 20 kilometers.
Amprius said it has shipped the first SiCore cells from its pilot line in Fremont, California, to several drone and UAV customers. AALTO, the Airbus subsidiary behind Zephyr, is one of them. Amprius introduced the updated SiCore cell in April with an energy density of 450 Wh/kg. The cell uses the company’s silicon anode material system and is aimed at aviation and other weight-sensitive applications. Amprius says the design can deliver up to 80% more energy than conventional lithium-ion cells based on graphite anodes.
That matters most for high-altitude platform systems, or HAPS, where every gram affects endurance. Zephyr flies on solar power during the day while recharging its batteries. At night, the aircraft depends entirely on stored energy for propulsion, onboard electronics, imaging payloads and communications equipment. In the stratosphere, that night segment can last 10 to 12 hours. Battery mass has long been the core constraint. Heavier packs cut efficiency, payload or endurance. Amprius says SiCore offers at least 50% higher energy density than standard cells, which can extend overnight flight, support larger payloads and improve weather margins. Those gains are central to the goal of keeping HAPS aircraft aloft for months rather than days.
AALTO said the silicon-anode cells support the lightweight and long-endurance requirements of its high-altitude missions. The company said the technology has already enabled Zephyr to operate overnight in the stratosphere for months at a time, a rare benchmark in persistent flight. Amprius, for its part, plans to expand pilot production in Fremont as demand rises from drone manufacturers. The company said it is now shipping both high-energy cells for HAPS missions and battery formats designed for a broader range of advanced UAV requirements.
If the qualification process leads to wider deployment, the new cells could strengthen the case for stratospheric UAVs as persistent platforms for surveillance, imaging and communications. The broader implication is clear: battery energy density is becoming one of the decisive technologies in next-generation unmanned aviation.