Thinking out loud here, with a good measure of ignorance added in:
I understand the idea of measuring the battery voltage at full charge to clarify this question of where the buffer sits, but
why not just compare the SOCs of locked and unlocked batteries where the charge rate rapidly tapers ? Seems like it should be good for a qualitative answer, which is I think all we need as a practical matter to be confident that routine 100% charging is safe for battery longevity.
Ambient temperatures probably change the taper point, but a decent data point size should sort that out.
Yes. That's what my previous post was trying to indicate. I was trying to match the 100% 60D charging rate to my 75D charging rate and see what my SOC is when the charging rate is the same. It seems like a 60D at 100% is at about 90ish % of the 75.