To avoid starting a new thread, I’m reviving this one:
There is no official statement by FP regarding any battery calibration process, or the need thereof. So I asked Support (mentioning the iFixIt page about calibration), and the reply was:
"You can do the calibration if you want, but with recent phones it is not really necessary.
So it should be fine both ways. "
OK, so this is unfortunately a bit vague, but at least they don’t advise against calibration. I had actually asked for more insights about how the battery management of my FP3 works, does it auto-calibrate during lifetime (and how does it do this?), does it recognize a new battery, etc. – but this is what the support person knew and had time for, it seems.
A word about overnight charging: Since this is quite convenient and common, I often use a “slow” charger and keep WiFi turned on, in order to delay and reduce the “unhealthy” time when the battery is at 100%. But I also regularly use fast chargers, mostly for convenience, but also to offer the battery a “varied diet”. Don’t know if that really helps, but my original FP3 battery still gets me through an average day after > 5y, so my strategy can’t be too bad 