Donut Lab Episode 15: 400 Wh/kg Claimed - VTT Tests It at 409 Wh/kg
- Paul Roberts
- 9 hours ago
- 2 min read
Since Donut Lab announced its battery, one question has come up more than any other: how much energy does the thing actually hold for its weight?
Now we have a number.
In Episode 15 of I Donut Believe, Donut Lab has released the results of an energy density test carried out by VTT Technical Research Centre of Finland.
The result is 409.3 Wh/kg. And that's slightly above Donut's long-standing 400 Wh/kg claim.
Skip to the video.
Read the VTT technical analysis here.
For more Donut Lab news, visit our Donut Lab page.
The Test
VTT was supplied with one Donut Battery cell, designated DL6. The research organisation weighed the cell, measured its dimensions, charged it and discharged it at 25°C within its recommended voltage range.
The capacity test used a 0.1C discharge rate, with the energy density calculated from the cell's measured weight, dimensions and the energy it delivered.
The result:
The result:
409.3 Wh/kg gravimetric energy density
804.7 Wh/L volumetric energy density
All test cycles were completed successfully, with VTT reporting no visible swelling or physical changes to the cell during testing.
One Important Detail
The cell tested wasn't simply described as Donut's V1 battery. According to VTT, DL6 was an energy-optimised version of the V1 cell, designated V1.5 to distinguish it from the cells tested in previous VTT reports.
That doesn't invalidate the result. VTT independently measured the cell's weight, dimensions and capacity to arrive at the figure. But it does mean we shouldn't assume every version of the Donut Battery V1 will deliver exactly the same 409 Wh/kg.
And there's another point worth making. 0.1C is not a high discharge rate. That fits with Donut's explanation that its cells can be configured around the requirements of a particular use case, with improving one characteristic potentially affecting another.
So a cell optimised for energy density might, for example, have a lower discharge rate.
We simply don't know yet how those different requirements affect each other.
The BCB Take
Let's be clear: 409 Wh/kg is a serious number. And it's a number that could potentially change how the e-moto sector performs and competes with other technologies.
Energy density was arguably the biggest unanswered question surrounding the Donut Battery. Donut claimed 400 Wh/kg, critics questioned whether the figure was even possible, and until now, we hadn't seen an independent measurement of that claim. Now we have.
On this particular test, the result actually lands above Donut's original claim. What we'd really like to understand now is how Donut's different claimed characteristics work together in the real world.
Donut has already said its cells can be optimised for different applications. So the bigger question isn't whether one cell can do everything at once. It's how those different optimisations affect the overall performance of each version, and, ultimately, what that means when the battery is actually sitting in a motorcycle.
Still, Donut asked everyone to wait for the energy density test. It's now here. And based on VTT's measurement, the number is exactly where Donut said it would be.
Roll on Episode 16.
Ride safe, folks.
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