The classic way to brute-force improve battery longevity was to create a hysteresis -- to postpone staring a charge cycle until the charged state had declined to a lower level, such as 92 percent, and when topping off, stop before 99 percent.
Catalina software 10.15.5 and later for MacBook Pro with T2 chip (2018 models and later) includes a feature called Battery Health Management. Now, based on your usage patterns, this widens the hysteresis to initiate a charge cycle at a lower level, and stop well before 99 percent.
About battery health management in Mac notebooks - Apple Support
About battery health management in Mac laptops - Apple Support
Battery Health Management feature tracks your usage history and detects that you do not generally run your battery down to low levels. So when you see less than 100 percent as a full charge, it is charging less than the highest level for longest battery lifetime.
NOTE that charging to 80 percent is a side-effect, NOT the GOAL.
The goal is to have some hurly-burly around using your battery, either by your actually using it, or by leaving it less than 100 percent charged, so that the cells are not 100 percent charged 100 percent of the time. Battery Health Management will also from time-to-time let the battery decline slightly to 'get some exercise' and run lower (thought to be around twice monthly) if you do not do so by your ordinary use.
The feature tracks you actual usage. If you continue to not require 100 percent charge for a few weeks, it generally will revert to a lower "full" level. but it takes some experience, which takes some time
If your recent usage patterns demand top battery capacity, the battery will charge completely to be sure you are not stuck out in the wild with no power.
