Okay, I found a solution to the battery pack for the Sony a6500 and other camera housings that used the now discontinued Nauticam 36331 iThin battery pack. It's a battery pack I found on Amazon listed as a Ultra Slim and distributed by many dealers under different names. The first one I received was marketed by " Kolumb "'. When I went to buy a 2nd, it's no longer available, but another identical unit is under the name " Attom Tech " NOTE: Turns out the Attom case is wider than the Kolumb case by and bit and won't work. Get the Kolumb power pack.
It's exactly the same battery under a different name. I tried to find a suitable battery on Alibaba and have a Chinese dealer/manufacturer looking for one that doesn't need modifications and has the same exact measurements and specs as Nauticam's iThin pack. So far he has been unable to find one. He actually proposed the same white plastic one I bought on Amazon. Apparently iThin no longer exist and why Nauticam discontinued the product.
The Kolumb Power Pack will work with just some slight physical modifications. It has exactly the same length and thickness as the Nauticam iThin, but it's 3mm wider at 61mm (the iThin was 58mm). This extra 3 mm will keep the rear door from closing correctly on the o-ring. The solution is to take a fine straight file and remove 3mm of plastic casing on it's sides. Most of it will come from the side where the built in USB cable nests itself when not in use, but some has to be taken from the side with the Micro USB power input charging port. You can also remove some from the end, but this is not absolutely necessary, but I did so to make it exactly the same length.
When finished the plastic on the sides will be paper thin, but still holds the case together. You can see in the attached photos where the top is starting to want to separate from the thin siding, so I will apply a drop of super glue to reinforce it. One of the options I didn't try was removing two rubber pads that help seat the original battery (see photo). If these were removed from the housing, they would allow for a lot less material being removed from the case, maybe 1-1.5mm. However, I didn't want to remove them from my NA-a6500 housing, so I filed the battery case sides down to 58mm.
The battery pack will shut itself down shortly after you finish charging and unplugging it. It will activate as soon as you plug it into the camera's Micro USB charging port and will stay active as long as it plugged in to the camera, even when the camera is turned on/off. In addition, it will charge the camera battery whether the camera is on/off. I tested the charge both ways and even checked to make sure it didn't shut off when the camera battery was fully charged, which was a problem mentioned above on the original Nauticam 1st generation battery. So this battery works exactly like the improved generation 2 Nauticam pack.
Besides the slight physical modification, one has to purchase a 25cm Micro USB extension cord. I had a hard time finding one the same length as the Nauticam with the correct angle (90 degrees-R angle (or L ? which was confusing due to bad pictures and descriptions on Amazon). I ended up buying a pair of one left hand and one right hand to make sure I got the correct one. The pair cost me $8 and the battery $12. Heres' a link to the 25cm cables: https://www.amazon.com/dp/B09SD5Z3MM?psc=1&ref=ppx_yo2ov_dt_b_product_details
The cable is routed exactly the same as the Nauticam unit. You plug the new battery's built in Micro USB cable into the new extension cord which has a 90 degree angle for plugging into the camera.
Took 15 minutes to file down the plastic case and you're ready to go. See the photos below for everything you need to do.
Finally more power for our cameras that are designed to work in housings with Nauticam's now discontinued battery pack. Should I get notice of another battery from my Chinese contact that works better, I'll update and let you know. For now, this one and it's cable are inexpensive at $20 and work just fine.
Good luck,
Marshall
