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.
