Only the D1 thru D6 and Z9 batteries may need calibration. I have used these for 18 years, may have done 5 calibrations IN TOTAL.So I guess the answer to the OP is to do it when it blinks to tell you to do it. Or if you have a model that doesn't tell you when to do it then do it on a schedule, like on the 31st day of every month that has 31 days or some easy to remember schedule, or to do it when the behavior of the battery in action makes you think something is wrong.
Now I'm glad I shoot Canon. Simpler.
No need to do it unless the charger blinks to do so, and ignore if you don't want to bother.
Fact is, the D1 may have not had a calibration, can't recall that far back. I do recall it was the flagship in 1999, 2.74MP camera body. I loved it.
I don't know about a Canon, I have never owned or used that brand.
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