Apple is about to introduce a new charging system for all MacBooks equipped with Thunderbolt 3 ports (so the Pro from 2016 onwards he Air from 2018 onwards). It's about the function Battery Health Management, which aims to extend the life cycle of MacBook batteries by reducing the number of times they are charged to 100%.
The most attentive will have noticed a particular similarity with the energy management policies introduced by Apple on iPhone (but not on iPad) with iOS 13. In particular we refer to the Optimized loading, which analyzes the user's charging habits to ensure that the iPhone battery is brought to 100% only when it is necessary (for example, overnight charging is blocked at 80% and reaches 100% in minutes prior to the user's awakening), in order to slow down the inevitable deterioration.
Starting with macOS 10.15.5 Catalina, a similar system will also be introduced on compatible MacBooks: the feature has already appeared in beta 2 released yesterday evening. In this case Apple will adopt a slightly different approach compared to what has been done with iPhone, especially as regards the percentages of residual charge that are shown to the user. In fact, the value attributed to 100% charge changes: this will no longer indicate that the battery has the maximum possible charge, but the maximum that it must receive in that specific condition.
As in the case of iOS optimized loading, in fact, the MacBook will only be fully charged when the system believes that it will soon be used for a long time away from the power supply. If instead a frequent use of the power supply for long periods, the battery will never reach its maximum recharge capacity (while continuing to show 100%) until the conditions and habits of the user change, all in order to prolong its duration over time.
The new battery management will be active by default following the update to macOS 10.15.5, however it will be possible disable it at any time to restore traditional behavior. If you choose to keep it, it will analyze the history of the data relating to the charging frequency, the battery temperature, the environmental one and the workloads to determine the most suitable charging scheme. All this data will be processed locally and some may be shared anonymously with Apple, provided that the user explicitly chooses to do so.
Finally, we report a final detail. On iOS we know that Optimized Upload limits charging to 80% while on macOS there seems to be no predefined threshold. Apple has not communicated this data, but it is likely that the limit may vary from device to device and to the health conditions of the battery, even if it is better to wait for clarifications on the matter.