How should I manage battery health when doing GPU-intensive work?

Your computer performs best when connected to AC power. It can use the full output of the Power Adapter AND when doing especially challenging work will also freely "borrow" power from the battery. In some cases, the charged state may even decline during stressful work.

When used only on battery, your computer has no extra cushion of power, and will perform more slowly. However, for ordinary non-stressful tasks this may not be objectionable (possibly not even noticeable.)

In general, you should ALWAYS connect AC power when it is possible to do so, and only run on batteries (which will be somewhat slower) when no AC sources are at hand. There are three micro-controllers cooperating on battery and charging issues, and your Mac will NEVER over-charge.

A charge cycle is ever-so-slightly destructive to batter longevity. When operating as designed (and not using Battery Health Management) battery charge level is allowed to decline to about 92 percent level before initiating a recharge cycle to top up to about 99 percent.

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Catalina software 10.15.5 for MacBook Pro with T2 chip (2016 models and later) includes a new feature called Battery Health Management. Based on your usage patterns, this widens the hysteresis to initiate a charge cycle at a lower level, and stop before 99 percent.

About battery health management in Mac notebooks - Apple Support

https://support.apple.com/en-us/HT211094

This relaxes the set points around re-charging (based on your usage patterns) and can improve long term battery lifetimes. When active, recharging may stop short of 100 percent charged.

Leave the computer pluuged in whenever convenient to do so. I don;t know where you are getting the erroneous advice about 30% - 80%. Neither your computer nor battery will be damaged by leaving it plugged in. The advantage of leaving the computer plugged in, besides improving your workflow, is that it will reduce the rate of accumulation of battery cycles.

That guy does not speak for Apple, Inc and has no "skin in the game"on this subject. As far as I am concerned, he is "just some guy", who happened to get his speculations up on a formerly well-known web site.

About a week after that guy made his pontifications, Apple issued 10.15.6 with Battery Health Management features.

'Battery Health Management' is the Apple solution to this problem, not what some guy posted on MacWorld magazine.

Gyro Gearloose wrote:

Thanks for the answers so far.

I found the article I got this from. It's by Glenn Fleishman "Don’t keep your Mac laptop charged to 100 percent all the time. Here’s why". [https://www.macworld.com/article/3564563/dont-keep-your-mac-laptop-charged-to-100-percent-all-the-time-heres-why.html]

That's not a recommendation from Apple.

So what has that got to do with Apple? I don't know what decade that author is getting his info from but it certainly does not apply to modern batteries.

You should read up on modern batteries and the Mac built in battery management function. I'll stick with my advice. Leave the computer plugged in when convenient to do so.