Will my battery redqueening strategy backfire?

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I have a new 2021 Macbook pro -- the kind that has magsafe again as well as allowing charging via USB-C. I kind of want to optimize battery health but don't want to think about it too much. Also I almost always use it at my desk and never leave the house. Apparently you shouldn't leave a laptop plugged in at 100% battery day and night. I hear that staying between 40% and 80% battery is optimal.

So I came up with this strategy: I charge my laptop with a phone charger that charges so slowly that when I'm using it it actually loses charge. But then I dim the screen a bit so it actually redqueens. I.e., the battery level stays constant indefinitely.

I mentioned this in the Beeminder Discord and gbear605 said she suspects that that's worse than leaving it plugged in with the normal charger. Something about the USB ports drawing power from the battery.

So that's my question. Is it better to just leave it plugged in at 100% day and night rather than charge it with a very slow USB-C charger meant for a phone that keeps it from getting above 80%?

I know that I could do better than either of those strategies, like by using software that keeps it from going above 80% battery, but let's assume I'm not willing to put in that much effort.

So this resolves YES if I'm better off leaving the magsafe charger plugged in 24/7 and resolves NO if it's better in terms of battery health to use a USB-C charger that keeps it below 80%.

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It seems we still don't have a definitive answer. Is it dumb to basically leave this open indefinitely? I'm still doing this over a year later and my battery seems fine?

Cycling 20-80 degrades the battery less (if the denominator is total battery power used, not number of cycles) than cycling 60-80. But it sounds like you mostly have it plugged in while you're using it, so it doesn't matter because you won't cycle the battery enough to degrade it.

@JonathanRay This doesn't match my understanding, but if you understand batteries better than me, I'm all ears. Do you know what it is about charging cycles that degrades the battery? How much worse is it to bounce between, say, 40 and 60 vs bouncing from 45 to 55? The latter means twice as many cycles but is it actually much worse? Is it the transition from charging to discharging or vice versa that degrades the battery?

I'm doing something similar with my phone.

It's used as a hotspot for 5-6 h a day via USB cable. USB 3.0 would charge it to a 100%, but I use USB 2.0, so it goes from 30-40% to about 80-90% with screen off and a few minutes of use. 100 or so cycles so far and I don't notice any capacity loss.

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I suspect "not worrying about it" causes less harm than the headache it saves you!

I think I learn new vocabulary every time I look at one of your markets Daniel. In this case "redqueening".

@Undox Ha, are you learning new vocabulary or just my esoterica? But, yeah, by redqueening I mean running forward but staying in one place, like Alice and the Red Queen in _Alice Through the Looking Glass_. https://en.wikipedia.org/wiki/Red_Queen%27s_race

Things I've learned in researching this: Looks like AlDente -- https://apphousekitchen.com/ -- is what's recommended if you want full control over this (stop charging at 80% etc). macOS has a built-in feature to try to be smart about it and learn your schedule and delay charging past 80% till it thinks you may want 100% which seems doomed if you just leave it plugged in 24/7. With the free version of this software it will keep your charge at exactly 80% which means lots of mini charge cycles between 79% and 80%. Unclear how bad that is. The paid version lets you control that too. Like "start charging when it falls to 70% and stop at 80%". They call it Sailing Mode. I've already spent more on this question than I'd have spent replacing the battery when it degrades in a few years. So that's dumb. But the original question stands if anyone can clue me in!

@dreev with older battery tech, mini charge cycles around a set point was definitely bad. I think it's less clear nowadays with modern batteries. That said, I'm skeptical of these kinds of fancy optimizations; there's a lot of pretty complex battery management circuitry and trying to outsmart it like this feels like a recipe for a bad time. How many years do you want your battery to stay good, anyway? is the time you spend fussing with this and thinking about it worth the $200 apple charges to replace the battery out-of-warranty, if it needs it 3-4 years down the line?

@Adam Small cycles to 80% are better than large cycles to 80% - good lithium-ion cells often provide info on this in their data sheets. Ideal is just to leave the battery as it is and use external power (and that's better for the battery if it's not fully charged) - which is what would happen if the proposed scheme was perfectly implemented. It's also what linux's change_stop_threshold sys entry does, but no idea what the equivalent on Mac is.