The batteries used in phones degrade quickest below 20% and above 80% of charge. This is already at room temperature. When the batteries or phone is hot the degradation at those state of charge (SoC) is even worse. In the car when using CarPlay the phone can get really warm, especially if it is in the sunlight which tends to happen easily. When left in the shade it gets hot due to restricted airflow.

Therefore I would like to limit the SoC on my phone to not excessively degrade the battery. I very rarely, if ever, need more than 80% of the design capacity of my iPhone anyway. So I prefer it to last longer.

Aren't there some internal safeguards already in place to prevent overcharging?

100% isn't over-charging. It's just not the GP's preferred spot on the battery energy (hours of charge) vs battery lifetime (days/years) curve for daily use.

I do wish phones would provide more control here. I would also take 80% charge many (but not all) days in exchange for my battery life after a year staying higher.

lmgtfy: Its the extremes (0% and 100%) that degrades LiIon the quickest, if you want the longest life ideally you'd keep it 30-70% the whole time, ymmv (and also thresholds).

And it is a pity manufacturers don't support you in doing stop-charging-at-x if you wanted, e.g. a simple thing for software to do, but impossible without rooting on Android.

ASUS Zenphone has a setting that lets you set a charging limit at 80, 90, or 100%.

Samsung S22 Ultra (at least) has a 'Protect Battery' setting which limits charge to 85% .

Its been a feature since at least the S9. Source: Had to 'fix' my girlfriend's phone only charging to 85%. Was a mystery how that setting got randomly enabled, really.

I can't recall for certain if my old S7 had that option but I don't think it did.

You're mistaken. Most Androids today have that charge limit function natively.