Due to the removal of the Ultrabay from nearly all recent models, the ability to use Ultrabay batteries were gone as well. Then came the Power Bridge, which was supposedly introduced to compensate for the lack of an additional battery.
As the battery charging and discharging behavior is controlled by the ThinkEngine chip, it cannot be modified by the operating system or through any means of software control. This is similar to how the Ultrabay batteries worked in the older models.
Note that there are two known ways of how the Power Bridge discharges batteries. For models that are older than the P51s, T470, T570, and the X270, the ThinkEngine chip will discharge the removable external battery first, before moving on to the non-removable internal battery. For models that are newer or are any of the models previously mentioned, the ThinkEngine chip will check the wear levels of both batteries before discharging the least worn-out battery in the machine.