FWIW, I usually followed Core's instructions to replace that battery about once per year. That never lead to a problem, taping about 3-4 shows a month.
I should also note that I stopped taping for awhile between 2000 and fairly recently. I got my old CSBs out and tried them... Still worked like a charm. I did replace the battery before trying at an actual show, though.
IMHO, replacing the 9v in the battery box is a waste of time/money/the environment.
I just a question for everyone. Usually I change my batteries for each show just because of the fear of the batteries dying during a set. But I am not sure when I should replace the 9V battery in my core sound battery box? What does everyone else do?