yeah I can tell you a little about that… so batteries don't "like" to be at 100% all the time, that actually ages them prematurely and could lead to swelling or explosion. That's why Apple introduced "optimized charging" for iPhone, where it'll stay at 80% charge all night, and only go to 100% about an hour before it expects you to wake up.
Swelling or explosion is unlikely, mind you, but not as unlikely as if you kept it at a more moderate number. (I actually heard about a guy who hooked up a HomeKit power switch to his charger, and set up an automation to turn it on when his laptop battery reached 20%, and off when it turned 80%… probably a ridiculous over-optimization, but very funny)
The first thing you should do is get
Coconut Battery. It will give you a much more detailed look at the quality of your laptop battery. I'm gonna paste in the report from my own right here… it's a one-year-old M1 MBP, I'm actually surprised to see it t 83% design capacity, that kind of sucks for this age. But that's what I get for keeping it at 100% most of the time.
The risk is that an old battery will develop "bubbles." Basically these zones of dead-space will appear in the battery, and your computer is no longer able to accurately read how much power is left. You might be sitting there are 80%, and suddenly it'll knock to 5%, and then die. And no, being plugged in constantly won't help; I had a neighbor with a truly dead battery in a Macbook Air, and kernel panic'ed constantly until I replaced the battery for her.
The rule of thumb is basically, if your battery design capacity is under 80%, replace it. If you use it plugged in all the time… you can probably get by with ignoring that until you get to like 50%, but don't be surprised if your Macbook just starts to get "weird."
p.s. Coconut Battery can give you detailed info on iOS battery devices too… I consider this one of those must-have power user apps.
