I am doing research on best practices for my lithium batteries and lifepo4 powerstation. There’s some conflicting opinions and variation for cycle numbers.
Will leaving my things plugged in at 100% hurt it more than constantly unplugging at 80% and replugging at 20%?
They don’t outside of not doing things that cause acute damage to the battery. They can’t because “best” is situational.
If I have a phone with an empty battery and I’m going out all day starting in an hour, best is to charge as fast as possible to 100%. That’s the most wear I could put on the battery out of any charge cycle, but going easy on the battery isn’t my first priority in that scenario.
On the other hand, if I have all night to charge and won’t be away from charging for more than a few hours the next day, best is to spend most of the night charging to 60% and stop there. It’s an order of magnitude less wear than the above, maybe more.
For best service life, avoid fully discharging[1] the battery, charging it above 60%, storing it long-term charged over 60%, getting it hot, or charging it in less than several hours. In most devices, you don’t have the ability to control any of that so the best you can do is plug it in at 20% and unplug it at 60% (or 80% if you need the extra runtime - it’s still better than 100%). I’d like to see consumer devices get an “eco mode” or some such to select battery-preserving behavior manually, but that’s not in the interests of device manufacturers who want you to buy something new when the battery wears out.
[1] An actual full discharge to zero volts causes acute damage to Li-ion batteries and most devices won’t let you do it