Apple in the second macOS Catalina 10.15.5 beta added a new Battery Health Management feature for Macs, which is designed to prolong the battery life and battery health of modern Mac notebooks (aka those with Thunderbolt 3 ports) by reducing the rate of chemical aging.
Battery Health Management is an intelligent feature that analyzes the battery status of a Mac notebook and its charging pattern, and based on this information, it may preserve battery health by not charging a MacBook to full capacity.
Charging a MacBook to 100 percent and then letting it sit plugged in without draining the battery through use can lead to reduced battery life, which is what Apple is aiming to avoid. Macs that are often used plugged in and with the battery full may have the Battery Management feature kick in to stop charging short of a full charge.
Read more at MacRumors.com