That's awesome to hear.
I have the voltaic batteries as well (V25, 6400 mah) and paired with their 5W/6v solar. I've got the solar panel mounted on the back off the post. I just made a tray of sorts and screwed on a ball joint hinge to the back. I mounted the panel in there and screwed that on to my post. I also have a Ring camera with a solar panel attached (and I've never had to to power the camera).
I get varied results. I'm in Seattle, so not as much sun in the non-summer months. And currently we're at the phase 2 (step on perch to open it) as we've got a set of new crows trying to learn it.
Between the crows and the stellar jays (of which there are 6 or 7, and greedy), they will jump on the feeder constantly until out of peanuts (usually within 10 minutes of refilling it), and then continue to jump more. So the battery gets quite a work out.
In the winter, I can make it 2 days or so. Summer, 4 or 5 days. I have a second battery that I just switch when I go to refill the peanuts.
When I've been at phase 3, it tends to last much, much longer....
Todd