Electronic Design has been keenly following the Donut Lab Solid-State Battery since its announcement at CES 2026. At first there was a high degree of skepticism, which was followed by speculation on how they might pull off their claims of 100,000 cycles’ worth of lifetime, extreme temperature operation of –30 to 100°C, and better than 400 Wh/kg of energy density.
Most of the world hasn’t been as kind in believing they have anything, forcing the company to do damage control by answering the widespread call for an independent verification of the company’s performance claims.
Today, a report on the Donut Lab SSB has been released by VTT, an allegedly independent measurement lab, also in Finland (which smells a bit lipeäkala). It shows real-world measurements on Donut’s submitted pouch cell, a copy of which we’ve appended to this article for our readers’ convenience.
The DUT (Donut Under Test, more commonly known as “device under test”) was specified as having a nominal capacity of 26 Ah at a 1C discharge rate, a nominal voltage of 3.6 V, and a nominal energy rating of 94 Wh. Tests were performed using a PEC ACT0550 battery cell tester, with the cell placed in a climate test chamber.
Testing revealed around 100 Wh of energy capacity at a 1C charge rate, and either 103 Wh or 106 Wh at 5C, depending on whether a one-sided or two-sided heatsink was used during the test.
At 11C charging rates, the cell exhibited around 101 Wh of energy capacity. Some configurations of minimalist heatsinking during testing hit the “safety limit” of 90°C.
So, yes, the DUT worked and clearly slightly exceeded published specifications, whether cherry-picked or a random “production” sampling. But here’s the rub — not one piece of data in that report matters other than perhaps the 90°C safety limit. Why?
Fake It Til You Make It?
Simple. The submitted cell could simply be an NMC pouch cell. The report doesn’t contain measurements of the cell dimensions or mass, which is basic and could be performed by a 10-year-old. The claims of 400 Wh/kg remain a total mystery. Charge cycles take time, but the number of charge cycles in this report are less than a dozen.
Despite being in a temperature chamber, all tests were performed with the chamber door cracked open, so more or less at room temperature. There also wasn’t any discernable cell confinement to prevent swelling, nor were any measurements made of before/after cell thickness.
In a nutshell, these independent measurements by VTT on Donut Lab’s submitted battery cell have proven absolutely nothing. Simple measurements like mass and dimensions were omitted from the report, which is a total headscratcher given the basic claim of 400 Wh/kg.
There may be more data coming, but this readout is an extremely disappointing nothingburger for anyone with an engineering/science background. It’s nothing but lay-cheerleader fodder, which no doubt will happily be done by some segment of the press.
Here’s a copy of VTT’s report for our readers’ convenience:
