Think of it this way: if you left your smartphone in a hot car on a summer's day and it not only survived but actually performed better, you'd be sceptical. That's roughly the situation Donut Lab is asking the battery industry to accept, and for the second week running, it has some credible data to back itself up.
The Finnish startup has released a second set of independent test results for its controversial solid-state battery, this time proving the cell can discharge at extreme temperatures up to 100°C and actually gain capacity in the process. The test was again carried out by VTT Technical Research Centre of Finland, a state-owned laboratory, continuing a weekly series the company launched in late February to counter fierce industry scepticism following its January debut at CES 2026.
For context, most conventional lithium-ion pouch cells face serious degradation and thermal runaway risk at these temperatures. The fact that this cell not only survived but delivered more energy is consistent with solid-state electrolyte behaviour, where ionic conductivity improves with heat because there is no flammable liquid electrolyte to decompose. In plain English, this means the battery runs cooler chemistry that actually likes heat, rather than being destroyed by it.
Donut Lab had originally claimed the battery operates safely from -30°C to 100°C with over 99% capacity retention. The VTT data actually shows the cell exceeding its room-temperature capacity at elevated temperatures, which is even better than the claim in absolute discharge terms. That is a result worth sitting with.
There is, as ever, a catch. After the 100°C discharge, VTT observed the cell pouch had lost its vacuum. The cell still functioned and charged normally afterward, but the outgassing suggests either the packaging or the cell chemistry produced gas at that extreme temperature. Whether that is a materials issue or a sealing problem remains unclear. For a company claiming production readiness, that is a detail engineers will not gloss over.
The backstory matters here. Donut Lab drew massive scepticism when it announced at CES 2026 that it had a production-ready solid-state battery with 400 Wh/kg energy density, 100,000-cycle life, and 5-minute charging. CES 2026 showed no working prototype, only 3D-printed mockups, which gave critics plenty of ammunition. The "I Donut Believe" transparency campaign, using VTT's independent reports, is the company's calculated response to those accusations.
Donut Lab is releasing VTT test results at a rate of about one per week, and both have confirmed specific claims. Last week's report validated the fast-charging performance: 0–80% in 4.5 minutes at an 11C rate. That result, verified by VTT on a 94-watt-hour pouch cell, is genuinely impressive. For comparison, Stellantis and Factorial's validated cells charged from 15% to 90% in 18 minutes, which was considered impressive at the time. Donut Lab's 4.5 minutes to 80% is in a different category entirely.
Now, before everyone starts celebrating the end of EV range anxiety, it is worth stepping back. Charging speed was never the claim battery scientists called impossible. Energy density and cycle life were. Neither has been independently tested yet. The 400 Wh/kg figure is roughly twice the energy density of Tesla's 4680 cells, and Yang Hongxin, chairman and CEO of Chinese battery manufacturer Svolt Energy, told Chinese media the battery "simply doesn't exist in the world" and called the parameters contradictory — though it's worth noting Svolt is simultaneously developing its own second-generation solid-state cells targeting the same 400 Wh/kg figure.
The competitive context is sobering for Donut Lab's ambitions. The biggest established players in solid-state batteries, including Toyota, Samsung SDI, CATL, and BYD, are all targeting 2027 or later for initial production of their own solid-state cells. None of them claim to have a production-ready cell matching all of Donut Lab's specifications simultaneously. Either the Finnish startup has leapfrogged the entire industry, or the full specification sheet will not survive scrutiny. The honest answer is nobody knows for certain yet.
There is a legitimate point in Donut Lab's favour that critics sometimes underweight: the company has actually submitted its technology to a credible, state-backed institution for independent testing and is publishing every result, including the unflattering ones like the pouch vacuum loss. By commissioning VTT to independently verify its claims and publishing the results through its "I Donut Believe" campaign, the company is at least doing the right thing in terms of transparency. That is more than many battery startups have done at a comparable stage.
CEO Marko Lehtimäki staked his reputation on shipping Verge Motorcycles with these cells in Q1 2026, a deadline that is now weeks away. Despite promises of Q1 2026 deliveries, Verge's CEO and website have confirmed that volume customer deliveries will likely stretch late into the year or possibly into 2027 as the company works through supply chains and regulatory approvals. That gap between ambition and execution is one investors and customers should track carefully.
Here's what this actually means for anyone following the electric vehicle transition: solid-state batteries genuinely matter. If an electric car could recharge to 80% in under five minutes, that would revolutionise the industry and make refuelling an EV about as quick as getting petrol, vaporising one of the key pain points keeping people from going electric. The promise is real; the question is whether this particular company can deliver on the full suite of claims at scale. Two tests confirm two things. The other four claims are still waiting. Watch the next VTT report closely.