I had the problem last winter. I first suspected that the battery was bad.. so I replaced it, then went in and reset the console to get rid of the message (just done and the down arrow or wait until midnight) and we are fine. I had thought maybe the solar panel was bad, as I also normally change the battery out. But it works fine.
What Davis suggested is that if the sunlight isn't hitting the panel long enough, then the super cap doesn't charge and it uses the battery more. We had not many bright days this last winter and I am guessing that is the problem. Anyway, I would take off the plastic cover over the ISS board and give it a look at the super cap with a magnifying glass to see if there is any corrosion or leaking. I live inland so there isn't much unless you ask about road salt during the winter, and there is no spray so that wouldn't be it for me.
If it cap is good then I would think it is either a bad series of batteries, or the solar panel isn;t doing its thing, or that the sun angle isn't charging the cap. IF it looks bad, then it is time to contact Davis to send you a new ISS board. What I would try to do is get them to send you the replacement board and you return the bad one to them. They have on their web site a video on how to replace the board. That alone tells me that you are not alone with these going bad.