Battery Expansion Expected Specifications

Obviously lots of posts here about additional battery capacity, I got curious just how much battery capacity would be added if the expansion bay housed an additional battery.

I’d prefer the battery expansion to not stick out any more than the default cooling shell so I’m going to use the default cooling shell schematics found here. Would be curious if people here share my preference?


  1. my dimensions were incorrect, see correction below by @Jacob_Padgett
  2. Framework CEO @nrp commented below with a more likely design which is much better

original post continued:
Using the Framework 13 battery for reference:
volume = 239mm * 6mm * 93 mm = 133362 mm^3 for 61 Wh

From the schematics I’m seeing a roughly 55mm by 60mm space between the fans in the expansion shell. The battery would probably be a little thicker (Framework 13 is 15.85mm vs Framework 16 is 18.95mm) so scaling proportionally would yield a thickness of 18.95 / 15.85 * 6mm = ~7 mm.

So the framework 16 expansion battery volume would be roughly
55mm * 60mm * 7mm = 23100mm^3
And using the same power density as the F13 battery we would expect the expansion battery to add…
23100mm^3 * (61 Wh / 133362m^3) = 10.5 Wh

Given the F16 comes with an 85 Wh battery this is a roughly 12% increase.

  1. is that math right? honestly not sure about the dimensions for the F16 expansion battery
  2. if this is only a 12% battery increase would you still want that expansion?
  3. how much extra space / weight would you be willing to give to a battery expansion shell?
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That seems really small, that’s 2x2 inches!

I don’t have the software installed to open the CAD files, but looking at this PDF from the GitHub repo, it appears that at least 110mm of battery could fit between the fans (118mm max, but perfect utilization may not be possible).

That gives nearly double your estimate. Still not a whole lot, of course.

I figured I’d use your method to calculate the capacity of a battery expansion that is as large as the GPU expansion.

  • Height: According to The Verge’s review, the fans in the GPU expansion are 11.5mm tall, so there would be as much vertical space for battery.
  • Depth: According to this Knowledge Base article, the GPU expansion adds 20mm of depth, for a total of 75mm.
  • Width: And, same as before, at least 110mm of width. The fans are still present, of course.

11.5mm * 110mm * 75mm = 94875mm^3 = 43.4 Wh (51% increase over the FW16’s main battery).

Note that this also creates the extra space in two places, which aren’t factored into my calculation because they aren’t suitable for battery:

  • Below the fans (3mm x 75mm x 75mm). A battery expansion does not need the 11.5mm tall GPU fans. However, it could use them anyway. The more powerful fans could run at a lower speed, and therefore quieter.
  • Behind the fans (11.5mm x 20mm x 75mm). A battery expansion wouldn’t need heat fins there, which is what I assume the GPU uses that space for. Again, not suitable for battery, but maybe it’d contain battery circuitry, or a couple USB ports.

The likely plausible path to enabling an extended battery is using a row of 21700 Lithium Ion cells that run along the back of the system. The area between the fans would then have the battery charging and safety circuitry. This would of course require a new Expansion Bay mechanical part to enable.


Thanks @nrp!

So with the F16 being 356mm wide and 21700 cells 70mm tall guessing framework could squeeze 4 (maybe 5) of them into a back row. If the cells are ~15wH each (<-- is that right?) that would be an additional 60 wH (maybe 75 wH) which is a huge increase of 70% (88%)!

The expansion would weigh 0.28kg (0.35kg) just from the 21700 cells so would probably be a little heavier than the GPU expansion (0.3kg) after battery circuitry is included.


Correct. Using 18650s would also be possible to reduce the size impact, but of course with lower total capacity.


So very interested in this.


Having them in a row on the back sounds super nice and very promising. I would’t mind the extra depth and weight.

That would leave the room in between the fans still free for people without GPU.

  • That empty space could then be combined with more heatsink material. One could exchange the bundled heatsink from the mainboard/CPU, and replace it with one that reaches into the empty expansion bay area.
  • And for the actual expansion bay, one could offer super high quality fans from for example Noctua.
  • The result would be more silent, with lower temperature, which would also benefit the internal/extended battery lifetime.

Dreams :star_struck:

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Honestly I’d be satisfied stuffing a Original FW13.5-equivent 45-55Wh battery inside the existing default or GPU expansion bay shells.

Boosting the internal battey capacity by 5-10% from 85Wh to 89-94Wh would be really nice too.


Same here

Hey all, we’ve been making a lot more headway on this HERE

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