Most of the issues with the ISS battery has been in either the charging circuit for the super-cap that kept giving me a weekly notice that the battery was depleted. Of course I replaced it always thinking , wasn't this unit be able to operate in total darkness for 3 months? I thought i read it somewhere.
so I started keeping a record of date/year/sensor when I replaced batteries. for those that are powered by the battery, I get sometime six months,maybe less. Now for the ISS, I figure if the summer or winter has been exceptionally nasty,to change the battery when that season ends. So it is possible every six months or a year at best .
I have 8 stations , I went big time. So I buy batteries in bulk. Cheaper for me. I go to Batteryjunction and I found that the Surefire brand seems to do a good job. of course I buy about 2 dozen at a time for about 1.50US each. Then when I start getting low,buy another set.
One advantage of waiting for the blizzard, it gets you out of the house for a while for some quiet time and it isn't that bad. For me my FARS has died off and I seem not to care. Probably the batteries have gone bad, but I really don't want to bring the unit inside to replace it, so we are going passive until I get to the point I need a project.