It took my MacBook Pro 3–4 weeks to learn that’s almost always used plugged in. Once it’s decided to cap charging at 80% you don’t need to run it unplugged to get it down to 80%: It’s smart enough to run on battery power even when plugged in to achieve this. Just be patient.

4 days later: Update on the MacBook Pro battery charging limit: After being unplugged and shut over the weekend, it decided to charge from ~79% back to 100% when plugged in on Monday. I feel like this feature to avoid battery degradation would work a lot better if it didn’t try to be ‘smart’.