Wedoany.com Report on Mar 10th, Finnish startup Donut Lab released the third independent test results for its solid-state battery on March 9, 2026. According to a report by the Finnish VTT Technical Research Centre, the battery retained 97.7% of its charging capacity after being left idle for ten days.

This solid-state battery previously sparked discussions about whether it belongs to the category of supercapacitors due to its outstanding performance data. Donut Lab's Chief Technology Officer, Ville Piippo, stated, "Since we introduced this battery, there has been considerable speculation. This test clearly confirms its battery properties."

The testing process showed that after being charged to approximately 50% state of charge, the battery was left at room temperature for 240 hours. Voltage recordings indicated that the charge loss was mainly concentrated in the initial period, with minimal decline after stabilization. The final discharged and recovered capacity reached 97.7% of the original value, verifying its low self-discharge characteristic.

This solid-state battery is designed for electric motorcycles and claims advantages such as fast charging and high energy density. The company had previously released fast-charging and thermal stability tests; this self-discharge test further supports its technical reliability. The VTT report noted that the test caused no visible impact on the battery structure.

Piippo added that while supercapacitors charge and discharge rapidly, they have a shorter charge retention time. In contrast, the performance of this solid-state battery aligns more with the energy storage behavior of traditional batteries, effectively maintaining its charge during idle periods.