External battery for Sony A7siii?

is cost an object?

The point of the Nauticam housing is its as compact as practical for the model.   There's not going to be room.   The Ikelites tend to use a more generic shell for many models, so there could be more slack space.

But you could do something with an external housing and route it through one of the ports, like the one intended for an external HDMI monitor.

Did you reach out to Nauticam or one of the camera shops that specialize on the production side?    Your wish isn't unusual for them, so there should be some solutions.

Thanks for the reply!

There is a bit of room above the hot shoe and that extra battery Nauticam made for the a7sii fit there, so I was hoping for something similar.

Backscatter suggested same as you, another housing for the battery:

https://www.youtube.com/watch?v=dkOkNySyWrg

I think this is the way to go but the next issue might be overheating with many hours of constant filming (24 fps, 1080p). I'll just have to try and see.

Ichthyologist wrote:

Thanks for the reply!

There is a bit of room above the hot shoe and that extra battery Nauticam made for the a7sii fit there, so I was hoping for something similar.

right...the well for the flash trigger.   You wouldn't be needing that.   I wonder if one of the OEM battery makers could be convinced to make a custom model that sit in the hot shoe and has the relevant wire leads.  Everyone getting this camera for UW use would want it.

Backscatter suggested same as you, another housing for the battery:

https://www.youtube.com/watch?v=dkOkNySyWrg

well, that looks great, and probably 1/4th the cost that Nauticam would want, but where's the price and vendor?

These are much bigger batteries than normal.   Seems like you would increase your capacity 5x.

I think this is the way to go but the next issue might be overheating with many hours of constant filming (24 fps, 1080p). I'll just have to try and see.

Has anything surfaced to date on this concern?   I'm in R5 land, where it's of course quite real, though I'd only get hit if running in LV too long still counts against me.   I'm going to selectively use the 4k/120, but not in any long sequences.    (Waiting on the GH6)

good luck!