Sony A7 III Interval shooting and battery life

[willfig]

I'm not actually and Alpha shooter yet but am hoping to be one soon. I have a rather unique application for the camera, which is taking 1000s of photos of coral reefs to build large area 3D models. We've done this lots with GoPros and more recently with full frame SLRs (Nikon D850 specifically). And we usually run multiple cameras at the same time (2 to 3) on a fixted mount system, swum around by a diver. I'm looking for a more compact system than the full frame and thus am looking at mirrorless options. One big issue I'm finding is battery life. We need to be able to take at least 3000s photos in a dive. The Sony Alpha's seem to be pretty good in this regards but Sony only lists expected shots in typical shooting situations and I think these far underestimate the number of shots that would be possible in interval mode. For instance a friend using an A6400, which is rated at about 400 shots, can definitley get 2500 out of one battery.

So my question to the forum is if any Alpha 7 iii owner has any experience with this or would be willing to run a test to see how many shots it can take on one battery. As for settings we would typically select our f-stop underwater (typically between 5 and 10) and set some limits on the ISO so it doesn't get too high. Then we set interval shooting at 1 per second or 1 per 0.5 second. So if anybody has any idea how the battery would last in this sort of scenario I'd be quite grateful. Thanks so much.