I used to swear by all these rules, and I’m SO glad to be over it. I picked up my 8+ a year ago last week. I’m at 99% battery heath, and I charge it any time I’m home and charge it to 100% while I sleep. Babying a phone in order to get an extra 6-12 months (at best) from it over the course of 3 years time is not worth it. If the battery couldn’t be replaced then by all means, yes. We’re talking about a battery that costs about $75 to replace, and even the most hardcore users will easily make it 18-24 months before needing it.
40-80% is a real thing. Lithium ion batteries prefer to stay at 70% at all times. It’s all true, it’s just not worth the hassle and I’m so glad to be over my battery ocd. I advise anyone on here who is dealing with it to just plug it in and force yourself to get over it. The alternative is maybe one extra battery over the course of 4 years of ownership, but most of us won’t keep our phones that long.