The watchOS 9.4 update that Apple is beta testing right now will include a battery recalibration process for the 44mm Apple Watch Series 6, Apple said today in an updated Apple Watch support document.
After updating to watchOS 9.4, the 44mm Apple Watch Series 6 will be able to estimate maximum battery capacity more accurately following the recalibration process.
Apple recalibrated the batteries of the Apple Watch Series 4 and Apple Watch Series 5 models with the watchOS 9 update, and now the process is being extended to the 44mm Apple Watch Series 6.