Donut Lab has released its third independent test report from VTT, the Finnish Technical Research Centre, and it confirms another claim: the solid-state battery retains 97.7% of its charged capacity after sitting idle for 10 days. This is a significant achievement, especially considering that standard lithium-ion cells typically self-discharge at a rate of 1–3% per month at room temperature.
['The new report adds self-discharge performance to the growing list of independently verified specs — but three reports in, the two most extraordinary claims remain completely untested. The self-discharge test followed a straightforward methodology, with VTT charging the cell to approximately 50% state of charge and then leaving it idle for 240 hours at ambient temperature while recording voltage every 10 seconds.', ['The results show that the cell dropped only 12 mV in the last 230 hours, indicating that the battery has essentially stabilized. This is a remarkable achievement, especially considering that solid-state batteries are theoretically expected to have lower self-discharge rates due to their solid electrolytes being less prone to parasitic chemical reactions.', ["However, it's worth noting that the self-discharge rate is not linear, and most of the loss is concentrated in the initial relaxation period. Extrapolated linearly, Donut Lab's 2.3% loss over 10 days at 50% SOC would put it in the 5–7% per month range — worse than typical lithium-ion. But the voltage curve shows a very flat profile from hour 10 to hour 240, suggesting that the long-term self-discharge rate is actually very low.", ["The three independent VTT reports in three weeks are encouraging, but there's nothing completely groundbreaking yet. Donut Lab continues to prove the claims that the battery industry considers achievable — fast charging, thermal tolerance, and 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.", ["However, the two specifications that drew the harshest criticism after CES remain completely untested: the 400 Wh/kg energy density and the 100,000-cycle life. VTT's reports have not included cell weight or physical dimensions, making independent verification of energy density impossible from the data provided.", ['The initial capacity test on cell DL1 measured 26.5 Ah and 91.8 Wh of discharge energy. If the cell weighs around 235 grams, that would put it near the 400 Wh/kg claim, but VTT does not report the weight, and calculating backward from an energy density claim is not the same as measuring it.', ["CEO Marko Lehtimäki staked his personal reputation on shipping Verge Motorcycles with these cells in Q1 2026. That deadline is now days away. Donut Lab's performance so far has been impressive, but there's still much to be proven.", ["The charge rate is probably the most impressive one, but moot as we see what's entering commercialization in China, such as BYD's second-gen Blade battery. We said after the first report that Donut Lab was proving the easier claims first, and that assessment holds after the third.", ["In conclusion, while Donut Lab's 97.7% charge retention is impressive, it remains to be seen how the battery performs under real-world conditions. The company needs to continue to prove its claims with more comprehensive testing, particularly on energy density and cycle life."], ' ']]]]]]]]
While Donut Lab's 97.7% charge retention is impressive, it remains to be seen how the battery performs under real-world conditions.
