battery capacity going down fast on 13 inch MacBook Pro

• Apple's general battery guide: Maximizing Battery Life and Lifespan
• Battery health management, highly recommend turning this on: About battery health management in Mac notebooks

I personally recommend keeping it plugged in all the time if it's not an issue for you. Of course this doesn't mean going out of your way and plugging it in even when it's inconvenient, but if it's stationary anyway, you might as well keep it plugged in all the time.

Lithium-ion batteries degrade faster when they're about 100% or 0% charged and when they're warm, even if the MacBook is off. Batteries also degrade when using them, deep discharges hurt them especially, e.g. going from 100% to 0% without charging.

Turning Battery health management on can help alleviating the problem of being charged 100% all the time while plugged in. It can automatically apply a capacity limit on your battery internally when it sees that it's plugged in most of the time, and this slows the battery's chemical aging. You'll still see 100% charged displayed in macOS I think.

Some people recommend taking it off the charger every now and then. I'm not an expert, but from what I know, this doesn't really do anything for the battery itself. Maybe it helps to calibrate the software that measures the battery's charge level and health, to display a bit more accurate data.

Apple's batteries are high quality, so they will last a long time, even longer if not used heavily.

You're not alone with the faster than advertised discharge. On the product page it says "10 hours wireless web" (this is vague, Apple says "The wireless web test measures battery life by wirelessly browsing 25 popular websites with display brightness set to 12 clicks from bottom or 75%.", but we don't know what they mean by browsing, maybe they just scrolled up and down a page). The Verge reviewed this MacBook 13" 2020 and got about 5 hours of battery life in a mixed use scenario, consisting of web browsing, Slack, Spotify, Mail, Lightroom.

The battery health degradation might be because you only have 4 cycles in it, there simply aren't enough data points. If it continues to go down at that rate (percents a week), that's a problem of course, but I'd bet that it won't continue this trend and the rapid decline that you see is more of an initial break-in or calibration phase.

I'm thinking that if you have the new "Battery Health Management" feature turned on, your Macbook Pro may deliberately be reducing your maximum capacity if you plug in often. Based on their description, it would reduce the maximum charge to make sure your battery is not charged at 100% too often, prolonging its battery life.

Same problem/ concern here... I have my MacBook since May in have some very worrying numbers ...