If it does battery pass through (supplying power directly from the outlet instead of using the battery as a middleman), leaving them plugged in should be fine. If it doesn’t the battery will repeatedly charge and discharge and and depending on the charge level limit that can be very degrading.

Charging the battery to 100% does do more damage than if you practice 20-80. However doing so limits the battery to 60% of its original capacity. Unless the battery is low quality or over stressed by default, it might take thousands of cycles until the gains from lower degradation outpace the losses.

I think the comfort factor is the most important tho. If you need to manually keep track of the battery and unplug it once it reaches 80% (and risk forgetting to plug it back once it gets low), just replacing the battery when it degrades might be the better option. If you can control it automatically, doing so would only be beneficial.

Copied from a different comment of mine:

well, you see batteries should not sit at 100% at all and if so, only if you start discharging immediately. So just getting them discharged and charging them again to 100% where they will sit at for 20h a day won’t help much against degrading the batteries.

"Choi 2002 shows that the constant voltage part is the most harmful to a battery, charging to 4.2V itself using constant current at 1C doesn't degrade it too badly, but by holding the battery at that voltage for an additional time causes most of the damage to the cell., [Source] (https://accubattery.zendesk.com/hc/en-us/articles/210224725-Charging-research-and-methodology)

I use a an App called Al Dente where I can set the maximum charge: https://github.com/davidwernhart/AlDente-Charge-Limiter

And there is also this: Basmati: https://github.com/aykevl/basmati

You can get it for windows too (googled that for you) https://www.thewindowsclub.com/battery-limiter-software-for-windows-10

For Linux my quick search found this: https://www.linuxuprising.com/2021/02/how-to-limit-battery-charging-set.html

Modern devices do this themselves, I guess through the EC (embedded controller). Best is to use an official or high quality charger with the exact fitting power.

Also if you have USB C, not every charger will have PD (power delivery) and recognize what power a device needs. For example I can charge my phone with my Thinkpad charger, but not any random cheap one

Every charging cycle ages the battery but worrying about it really isn’t worth the hassle.

If this is an Android phone, go install Accubattery and do what that says. It’s designed for many different phone batteries and associated tech (e.g. overcharge circuitry).

There are so many different models and variations in the electrochemistry, general advice is usually a miss.

If you insist on generalizing lithium tech, keep it between 30-80% charge for good longevity. The extremes of full and empty are rougher on it.

Title says plugged in and body says plugged in at 100%; these can be separate concepts if one has fine control over the charging voltage.

Will leaving my things plugged in at 100% hurt it more than constantly unplugging at 80% and replugging at 20%?

Plenty of academic research out there showing that pegging Li to 100% SoC reduces cycle counts to EOL (by electrolyte degradation and other processes), especially at higher voltages/temps. You didn’t mention capacity reduction associated with charging at freezing temps so I assume that is a non-issue in your use case.

It seems to me that if leaving it plugged in is an option you have shore/mains/grid power. So I’d

• charge to middling SoC and unplug the powerstation (according to the manual); and
• run the loads off the wall socket

Am I missing something here?

offgrid with LiFePO4

I live offgrid with Li on a very limited budget, so performance and maximal cycle life is a practical matter for me. Based on my own reading and experimentation I charge my 4S LiFePO4 to 13.8v (3.45Vpc) until Absorption falls to 0.10C then quasi-float at 13.31v (3.3275Vpc). I warm them to 50F and charge at ≤0.4C.