I started another thread earlier about my dummy batteries reporting they were running down in an A7IV, which ... is weird, because dummy batteries don't have any actual capacity. I've since done a bunch more testing and googling, so I figured I'd start fresh here.
Checking around on some forums, Youtube comment threads and so forth, I've found several other people experiencing the same. None said they were using the official Sony dummy battery (and neither am I), so it's hard to tell if that would act differently. None seemed to come up with a definitive solution, though some used combinations of power adapters and dummy batteries they said slowed the progression to a point it was usable. All seemed to be using fairly recent Sony cameras - a6400s, A1s, etc.
I'd never experienced this issue before on my a7iii or a7riii.
A dummy battery should, in theory, result in a report of a consistent output to the camera, whether that's 100% or otherwise. As I understand it (please correct me if I'm mistaken), the output is tied to the voltage. A real battery, though rated for 7.2V, actually may have output as high as 8.4V when fully charged and considerably lower when running down. In most places I've seen, it's generally considered safe to use a power adapter providing between 7.2V and 8.4V with a dummy battery for Sony cameras (and some that are packaged with them do indeed provide as much as 8.4V). Most people caution against going higher, even though electronics usually have a little flex with voltage. One might be able to safely run a camera at 9V, but I wouldn't try it myself.
I'm not 100% clear what a "fully decoded" battery does, though some are advertised as such. My limited understanding is that they report their status to the camera in some way, and are less likely to be seen as incompatible by the camera (which can result in a warning or the camera simply refusing to power on, depending on the model). I'm not sure if they also regulate a report of capacity.
I started with two dummy batteries I had, not knowing if they were considered "fully decoded" or not. I also had several power sources, including an AC adapter originally provided with one (with a stated 7.4V output), a USB(A)-to-DC adapter (which converted the 5V USB source to 7.2V, and needed at least 2.4 amps at the source, with a stated 7.2V output), and a PD USB(C)-to-DC adapter (which needed at least 18W total at the source, with a stated 8.4V output).
I also purchased a third dummy battery that was indeed advertised as fully decoded.
ALL combinations still result in the reported battery level slowly going down on my two A7IV bodies, eventually reaching 0 and then, after some time, shutting the camera off. None exhibited this behavior on my older cameras. But the particular behaviors varied slightly.
* With the USB(A) adapter and any combination of dummy batteries, the camera would power on, but shut off sporadically, though it had worked fine with the older cameras. I suppose the actual power draw on the a7IV may be slightly higher than the a7iii or a7RIV and too much for this solution. This was, in a USB-A charger that should have been able to provide at least the stated required 2.4A; I tried a few with the same results.
* One of the two original dummy batteries would result in a warning that the camera couldn't guarantee the safety of the battery; the other wouldn't. On the first one, whenever the warning popped up, it would also stop showing a specific percentage for the battery level, but only the graphical battery indicator. The second dummy battery continued showing the percentage. My newly purchased "fully decoded" battery acts like the second did. I'm presuming my second one was indeed fully decoded as well, resulting in the different behavior between the two.
* When I use a universal DC adapter at 7.5V, the reported battery level starts off in the low 80-ish percentage range, and then slowly declines. The adapter's next level down is 6V and next level up is 9V, so adjusting further isn't an option unless I want to risk giving the camera too much juice. The AC adapter that had been included with one of the dummy batteries showed similar behavior.
* When I use the USB(C) adapter that starts with an 18W source and was advertised to provide an 8.4V output, the camera reported 100% battery at the start of use. This seems to makes sense, because reported capacity is tied to voltage. It still declined, but I think more slowly than with the other combinations.
The reported level can be reset to its starting point with any of these solutions by removing the power source and then plugging it back in. So the last solution is workable for me, for now, because it "drains" so slowly that it won't hit 0 in any one sitting I'm likely to have (even a very long video call over the new UVC function or other video production).
But it's still a mystery to me why the indicated capacity goes down at all, and I wonder if it does the same with the official Sony dummy battery (which is too expensive to be worth trying unless I couldn't find any other solution).
