Third Independent Test, Third Verification
Finnish battery startup Donut Lab has released its third independent test report from VTT, Finland's Technical Research Centre, confirming another specification of its solid-state battery technology. The latest test verifies that the battery retains 97.7 percent of its charged capacity after sitting idle for 10 days — an impressive self-discharge rate that places it among the best performers in the battery industry.
The test report, designated VTT-CR-00125-26, adds self-discharge performance to a growing list of independently verified specifications. Previous VTT reports confirmed the battery's energy density and cycle life claims, building a methodical case for the technology's viability in real-world applications.
However, the pattern of selective verification has drawn attention from battery industry observers. Three reports in, the two most extraordinary claims Donut Lab has made about its technology remain completely untested by independent laboratories.
What the Test Actually Shows
Self-discharge rate measures how quickly a battery loses charge when it is not being used. All batteries lose some charge over time due to internal chemical reactions, but the rate varies dramatically by chemistry and construction quality. Lithium-ion batteries typically lose 1 to 5 percent of their charge per month under normal conditions. Donut Lab's 2.3 percent loss over 10 days translates to roughly 7 percent per month, which is competitive but not exceptional for a solid-state design.
The significance of the result lies more in what it confirms about the battery's construction quality than in the absolute number. Consistent self-discharge performance across cells indicates that Donut Lab's manufacturing process is producing batteries with uniform internal properties — a critical requirement for scaling production beyond laboratory prototypes.
VTT's testing methodology involved charging the battery to full capacity, disconnecting it from all loads, and measuring the remaining charge after 240 hours in controlled environmental conditions. The test was conducted on multiple cells to verify reproducibility.
The Unverified Claims
Donut Lab has made two claims about its solid-state battery that would, if true, represent genuinely revolutionary advances in energy storage. The first is an exceptionally high energy density that would significantly exceed current lithium-ion technology. The second involves charging speeds that would dramatically reduce the time needed to replenish a depleted battery.
These claims have attracted significant investor interest and media attention, but independent laboratories have not yet been given the opportunity to verify them. Battery industry veterans have noted that extraordinary claims about energy density and charging speed are common in the startup world and rarely survive rigorous independent testing.
Donut Lab has said that additional testing is planned and that it is working with VTT and other laboratories to verify the full range of its specifications. The company has not provided a timeline for when the most critical claims will be independently tested.
The Solid-State Promise
Solid-state batteries replace the liquid electrolyte in conventional lithium-ion batteries with a solid material, which offers several theoretical advantages. Solid electrolytes are generally less flammable, potentially enabling safer batteries. They can also support the use of lithium metal anodes, which offer higher energy density than the graphite anodes used in most current batteries.
Major automakers and electronics companies have invested billions of dollars in solid-state battery development, with Toyota, Samsung SDI, and QuantumScape among the most prominent players. However, manufacturing solid-state batteries at scale and at competitive costs has proven extremely challenging, and no company has yet achieved mass production.
Donut Lab's approach uses a proprietary ceramic electrolyte that the company says can be manufactured using modified versions of existing battery production equipment, potentially reducing the capital investment required for mass production. If this claim holds up, it could address one of the biggest obstacles to solid-state battery commercialization.
What Investors Should Watch
The systematic approach to independent verification is both a strength and a source of concern. On one hand, Donut Lab is doing something that many battery startups fail to do: subjecting its technology to credible third-party testing and publishing the results. On the other hand, the selective order of testing — verifying the least controversial claims first while deferring the most extraordinary ones — is a pattern that experienced investors recognize as a potential red flag.
The battery industry has seen numerous startups generate excitement with promising early results only to fail when their most ambitious claims were put to the test. Until Donut Lab's energy density and charging speed specifications are independently verified, the company's technology should be regarded as promising but unproven in its most critical dimensions.
This article is based on reporting by Electrek. Read the original article.
