> The main culprit is that anyone estimating battery life in percentages.

I thought this was a solved problem, like, decades ago? At least I remember even the first gen MacBooks having accurate battery percentages, and it’s a more vague memory but my PowerBook G4 did too I think.

The "accurate" charging level mostly happens with specific amount of charge cycles (i.e. new). Laptop batteries suffer from higher temperature (over 60C), overcharging (over 4.22 per Li-Ion for most chemistries).