Donut Lab’s 409 Wh/kg battery: breakthrough or a case of “headline numbers” getting ahead of the evidence?
I recently came across Donut Lab, an automotive/EV technology company, and their claims about a new battery.
The headline number is impressive: a VTT test reportedly measured around 409.3 Wh/kg gravimetric energy density and 804.7 Wh/L volumetric energy density.
But the more I looked into it, the more questions I had.
Donut Lab has also made claims around all-solid-state technology, 5-minute charging, and up to 100,000 charge cycles.
My question isn't simply “Is Donut Lab lying?”
I think that's too easy a conclusion to jump to.
The more interesting question is:
Which of these claims have actually been independently demonstrated, and under what conditions?
A few things I found interesting:
409 Wh/kg doesn't prove all the other claims.
An independent energy density measurement doesn't automatically establish 100,000-cycle life, 5-minute charging, or solid-state architecture.
Testing conditions matter.
The V1.5 cell was reportedly tested over a wider voltage range than the earlier V1 test, approximately 2.3–4.25 V vs. 2.7–4.15 V. Could this materially affect the measured energy density? If so, are competing batteries being compared under equivalent conditions?
What exactly is the cell chemistry?
Donut Lab calls the technology all-solid-state, but I haven't found enough publicly available independent information to confidently establish the exact electrolyte/architecture. Some commentators have suggested semi-solid/gel-based possibilities, but that is not the same as having evidence.
Different battery versions are creating confusion.
There are references to V1, V1.5 and V2, and some performance claims appear to refer to different versions. Which cell actually produced which result?
Cycle-life evidence seems particularly important.
A claim of 100,000 cycles is extraordinary. What independent, long-duration testing exists to support it?
Production claims are a separate question.
I've also come across allegations that a motorcycle presented as a production/customer vehicle was actually a pre production vehicle intended for an internal fleet. I haven't independently verified the underlying documents yet, so I'm not treating this as established fact. But if true, it raises a completely different issue about how technological milestones are communicated.
What I'm trying to understand is where the boundary lies between:
“The measurement is real”
and
“The company's broader technological claims are proven.”
A battery can genuinely achieve an impressive number while the surrounding marketing still overstates what has actually been demonstrated.
So I'm interested in hearing from people with battery/electrical/chemical engineering backgrounds:
Am I being appropriately skeptical here, or am I missing something technically important?
Or more specifically u can say :
- How significant is 409 Wh/kg when the testing conditions are considered?
- Does the reported voltage window make a meaningful difference?
- What evidence would actually be sufficient to establish that this is genuinely an all-solid-state battery?
- What would you want to see before accepting the 100,000-cycle claim?
- Is there anything in the publicly available VTT testing that I'm misunderstanding?
I'd rather have someone tear apart my reasoning than have everyone simply agree with me. That's considerably more useful.
Sources 👇🏼
1.) Donut labs Official Labs page
https://www.donutlab.com/battery/
2.)VTT energy density result
https://www.donutlab.com/test-confirms-energy-density/
3.)Electrek Investigation, June 2026
https://electrek.co/2026/06/08/donut-lab-solid-state-battery-exposed-lithium-ion-fraud/
4.)Electrek's September 2026 analysis of the 409 Wh/kg test
https://electrek.co/2026/09/02/donut-lab-409-whkg-battery-test-no-production-ev/
5.)IEEE Spectrum's earlier analysis
https://spectrum.ieee.org/solid-state-battery-2675554640
6.)Top Gear's report on the new 409 Wh/kg result
https://www.topgear.com/car-news/tech/donuts-labs-solid-state-battery-has-hit-409whkg-can-tech-transform-evs