I've been at the cabin, on solar power, for a year now. I have a year of data!
Everything went pretty well until last month. There was an April rainy spell where power felt slightly tight. Then over the summer, plenty of power, no need to conserve. The last month though had what seemed like weeks of continual grey clouds, where I never saw the sun.
Of course, even on a sunny day in winter, it does not get far above the hills, and the peak production window is only a few hours. This bad combination had my battery power dipping below the 10 volts that I consider low, down to 9, and even to 8 volts.
I use kerosine lamps in the winter. (I prefer the light anway.) I've also started unplugging my Thecus server at night to conserve power, meaning no internet late or early. For four or so nights, I had no power to run even my laptop after sunset. On one notable day, there was no power even in the daytime.
Even when it turned sunny again, I found that the batteries would seem to charge to 12 volts during the day, but then precipitously drop to 10 and 9 volts at night. I think the problem was not damaged batteries, but that these Nicads charge most efficiently above 12 volts (14 volts is best), and there was never enough power saved up to get them full enough that they could charge really efficiently.
So, I reluctantly spent three days away this week, to let the batteries soak up sun and recover. It seems to have worked; they've been holding a 12 volt charge overnight again.