Well there's no doubt that
Well I can tell you from my own experience.
1. I'm charging my company iphone always 100 by night. After 12 months ios shows already lost of 15% in capacity and I'm getting shorts sot already.
2. In my company (that I work for 16y) we use lenovo ThinkPad laptops. On begining like all ppl we use them 100 to 20% mostly. IT need to change batteries every year. After New policy and lenovo vantage options we now use charge to 80% and not charge if battery is higher than 30%. Now IT need to change our batteries every 3 or more years and on my p53 after 3 y I have still same SOT I was have on begining. And company save aaaaa lot money for batteries as ws we have tons of laptops.
3. I have a RC hobby. I fly with 3D helicopters, boats and planes. I use lithium polymer batteries, as for maintanance they are same as li ion. I'm in my hobby for 16y now. Some of my batteries that are F expensive have now 8 y and only 5% loose in capacity. The only rule is do not discharge below 20% and do not left it full for longer than needed (we charge them full just before flight and flight takes 5 minutes) . I use digital chargers that gives info how many mah I can put back to them so in example 2200mah bat after flight have like 400 mah left and I still put 1500 mah I. 8 y old bat.
So yes. The last 15% is wearing battery more than charge often to 85%. As battery reach full capacity the higher is voltage and resistant during charging. Resistance is a key as it makes permanent wear on electrodes. The lower resistance the longer battery life. It is just chemistry.
With my old s10+ that I never discharge below 30% and mostly charge to 85% after 4y I only loose 1h of sot...
I completely agree that there are certainly many ways to "save" battery health, and how you describe the above (in quite a wide variety of scenarios and not even quoting Samsung devices in a comparative way) is probably not the most optimal way to do it either - that is, you could probably save even more, but inconvenience/impracticality would start becoming an issue. However, the question is whether it's worth changing approaches at all specifically for Samsung devices.
I know for Electric Cars, some batteries are much better at reducing degradation than others. Generally, there have been significant improvements all around as battery tech improves. The Blade battery for example is so good at reducing degradation that the manufacturer/sales companies don't bother suggesting/recommending their customers charge to 85-90% only like many other brands do.
I can't speak for the iPhone or for laptops/tablets (also wouldn't surprise me if you're using old models which have older anti-degradation battery tech etc), but I can share my real-world experience with having owned 3 previous Samsung phones (prior to S23 Ultra). With the S7 (owned for 2-years) and S9+ (owned for 3-years), I observed what I'd subjectively say as mild degradation by charging to 100% overnight (and thus leaving it "on charge" at 100% for at least 4-6 hours a day). I use the term "mild degradation" as it did not impact my everyday use of the phone at all in terms of battery life. This is what is actually important, rather than measuring some number with some app which may or may not be accurate.
With the S21 Ultra (owned for 2-years), I actually stopped leaving the phone charging overnight, but always topped up to 100% in the evenings (before bedtime) and then disconnected the charger once it hit 100%. That would be the only period of time I'd charge the phone on the vast majority of days. When the phone was brand new, the estimated battery life reported by Device Care ("A full charge will last about") was 2 days and 2 hours. 2-years later, it remains the same. However, more importantly (as referenced above), I also noticed no change in everyday use of the phone in terms of battery life.
Anyway, it's possible that Samsung battery tech is better than (older) iPhone models and other laptops. Who knows really. But anyway, I still don't see any compelling reason to only charge to 85% for my specific use case, but it's interesting to read about other people's experiences.
