Technology

I don't like this article because it misses some of the more important details around how to lengthen your device's life and why you may or may not want to keep your battery at a specific state of charge.

1. State of charge is pretty arbitrary, your charging circuit could charge between 3.0V and 4.2V (pretty typical), or it could charge between 3.2V and 4.0V and still show 4.0V as being 100% charge. Different chemistries can have slightly (or significant in the case of LFP) different voltages. The cynic in me wouldn't be surprised if eventually 100% becomes ~4.35V because it makes their device look better to tech reviewers, but then have it default to only charge to 4.2V because it still gives suitable device life.
2. The most important factors in how long your device's battery will last are temperature and how deeply you discharge the battery. Discharging your phone down until it dies does way more damage than keeping it charged at 100%.
3. At some point practicality comes into it, you would get even more total energy out of a cell if you kept it between 40% and 60% all the time, but obviously it isn't very practical to only use 20% of your phone's available capacity in day to day use.
4. Consider how long you are storing your device. If it is always plugged in or won't be used for months, then something like 40% to 60% would be a more suitable state of charge to keep your device at if possible. If it sits on your desk and you need to unplug it periodically and know you don't need the full charge, then sure keep it at 80%.

Personally, I don't stress about the batteries in my devices at all. I generally keep an eye on the power and plug it in when convenient, but target plugging it in before it gets too far below 50%. I've historically had almost zero issues with the batteries in my devices wearing out before I'm ready to replace it for other reasons unless it started out with marginal battery life.