Finnish battery startup Donut Lab released its fifth independent test result this week, documenting how its solid-state battery performs after structural damage. The results offer little reassurance about the cell's long-term durability, and the test adds to a pattern that has frustrated battery industry observers.
The test specifically assessed whether the damaged cell could function under high charge and discharge currents; the short answer: barely. VTT cycled the cell fifty times at 5C (130 amps) between 0% and 90% state of charge at room temperature. The initial 1C discharge capacity measured 24.689 Ah, but after just six cycles at 5C, the capacity began dropping sharply. By the end of 50 cycles, it had fallen to 11.194 Ah — a 54.66% reduction.
The damage in question occurred during an earlier high-temperature test. During a previous 100°C high-temperature discharge test, the cell's pouch lost its vacuum — a significant structural compromise for a solid-state cell that relies on tight mechanical contact between layers. The test was a demonstration of the Donut Battery's ability to operate safely when damaged, and during standard 1C charge and discharge cycles, the battery cell operated completely normally and safely, even though its vacuum structure was broken.
The interpretation of these results reflects a fundamental tension in how Donut Lab and independent observers assess its technology. According to Ville Piippo, CTO at Donut Lab, if a similar failure occurred with a traditional lithium-ion battery, liquid electrolyte would leak out and active materials would come into contact with oxygen, potentially leading to fire or thermal runaway. Lithium-ion batteries would no longer operate after vacuum loss, whereas the solid-state cell continued functioning. This framing emphasises safety benefits rather than addressing the steep capacity loss.
However, five independent tests into its verification campaign, a critical gap remains. Not a single VTT report addresses the two claims that actually matter: the 400 Wh/kg energy density and the 100,000-cycle life. Verifying energy density requires simply weighing the cell and measuring its output — a straightforward test. Yet five reports in, no independent party has done it.
The test pattern itself invites scepticism from industry analysts. Donut Lab continues to prove the claims that the battery industry considers achievable — fast charging, thermal tolerance, low self-discharge. These are engineering challenges, not physics challenges. Solid-state batteries, by their nature, are expected to perform well in all three areas.
CEO Marko Lehtimäki staked his personal reputation on having these batteries inside production Verge Motorcycles by the end of Q1 2026 (31 March). Verge Motorcycles CEO has said first deliveries would begin in late March, but EU and US safety certifications are still pending, and the company has limited 2026 production to approximately 350 motorcycles. With the deadline now just over a week away, the company faces pressure to deliver tangible proof of its claims or acknowledge delays.
The broader context is crucial. None of the established players including Toyota, BYD, CATL, or Geely claim to have a production-ready cell today with all of Donut Lab's specifications simultaneously. That's either because the Finnish startup has genuinely leapfrogged the entire industry, or because its full set of claims won't hold up under comprehensive testing. As of 2026, the solid-state battery market has yet to reach scalability and commercialization.
Donut Lab has taken more transparency steps than most battery startups, publishing test results through its I Donut Believe campaign. Yet the selective focus of these tests, combined with the absence of the single most easily verifiable claim, suggests a company managing perception rather than building confidence through comprehensive evidence. The battery industry and potential customers deserve either full transparency or candour about why the most extraordinary claims remain unverified.