Earlier quoted context omitted.
> The battery is wearing out a bit, but it started out life with so much runtime that losing a few hours doesn't seem to matter. this is my exact opposite experience. my M3 Max from 2 years ago now has <2hrs battery life at best. wondering if any experts here can help me figure out what is going on? what should i be expecting?
Charge habits with batteries make a huge difference. If your use pattern is that once per day, you take the device from 100% to 10%, you put a lot more wear on the battery than if it kind of hovers in the 30%-80% range for example, or if it just hangs out nearish top-of-charge all day when you're at your desk. Hot take: people should get used to, and expect to, replace device batteries 1 or 2 times during the device…
> Hot take: people should get used to, and expect to, replace device batteries 1 or 2 times during the device lifetime.
I agree that people should get used to replacing device batteries, but if you accept that then you should just stop worrying about charge habits. An MBP that doesn't have a defective or extreme-heat-damaged battery should stay above 80% battery capacity for at least 600 charge cycles without any special care at all. That's many years of regular charging, and 80% capacity is still good for all day usage.