I used to put the battery of my old MBP under charge when it dropped under 40%.
Now, on the NET, I read that, with this new generation of MBBAir, the power adapter may stay always plugged-in confortably: They say that even Apple says this will not harm the battery in any way; nor will it harm the life-cycles of the battery itself.
So, what’d be your recommendations? When working, always under charge? Or only when battery level is below 40 %?
Keep it in charge whenever you can.
Unplug at night if the Macbook is sleeping/turned off.
I leave my M1 plugged in as much as I can. The new software generally doesn’t charge it over 80%, which is what saves the battery.
If I know I’m going to be running off battery for a long period, I’ll force it to charge to full an hour or two before I leave.
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I never heard about a 40% thing, even when I was working at Apple…
The Apple Power supply is not as dumb as people believe. It charges the battery, then when it is at 100%, it polls the battery to check it is stil at 100% (trickle mode) until the battery charge drop below 95%. Then, It charge it back to 100 % (This may have changed because sometimes I can see the charge is not at 100% but the MenuItem allows me to force the complete charge in case I have to go off Desk / Home).
Do not read Windows / Linux informations web site: they know nothing about Apple 
PS: removing the battery was a bad, really bad idea. Apple never talk about that !
What would happens if a micro cut of electricity happens then ? You lost your not saved work. If Apple glues the battery…
With modern batteries, combined with a few OS features, you really don’t need to worry about this sort of thing anymore. I typically have my MBA on charge whenever I’m near a power socket. Sometimes that’s all day or several days, and sometimes I happen to drain the battery completely. With Apple Silicon Macs (like your new one), Optimised Battery Charging is on by default, with Intel MacBooks, you can switch it on in System Prefer… Settings. This feature will try to figure out your charging patterns and manage charging to 100% for you.
The only thing I’d really do is ensure it’s not permanently on charge - i.e. actually use the battery now and then, but I wouldn’t be worrying about it on a day to day basis
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Alternative to the automatic built-in to macOS, you can manually control it with the Al Dente app:
Since I got an EV this year, I’ve learned way more about batteries than I wanted to. Li batteries prefer not being at 100% or 0%. Generally, it’s better to charge in a smaller range of SoC. So with my car, when it gets down to 30% I charge it back up to 50% (I don’t drive that much). With the limits of MacOS, I would definitely only charge it to 80%. I do this with my iPhone, plugging it in every night.
Not sure what you mean by “the limits of MacOS”, but Optimised Battery Charging does just that, it takes the battery to 80% then figures out, over time, when you might unplug it, so that it can intelligently take it up to 100% when the time is right, rather than sitting at 100%. Same as the iPhone. As I said, you don’t have to worry about this stuff nearly as much as you used to - different battery technology, smarter OS.
Got it, loud and clear. Thank you all.
Care to share link to Apple web that document that ?
You are correct, what I meant to say is to use the 80% setting to limit the time at 100%.
It should be noted that the Apple user interfaces are inconsistent for various devices. Some devices have an explicit 80% setting, and some only have the option to “optimize“your charging, which eventually will settle on 80%.
What’s an EV, please?
Electric car.
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Thank you.