Set the macOS power mode
Open System Settings, choose Battery on a notebook, and select Low Power Mode from the On Battery energy-mode menu when the option is available. Apple documents separate choices for battery and power-adapter use, so decide which state you actually want to change rather than assuming one choice applies everywhere.
Low Power Mode may change performance or other behavior in exchange for lower energy use. It is appropriate when longer runtime matters more than maximum responsiveness. Check the Battery or lightning-bolt menu-bar status to see whether a power mode is currently on.
Check model and workload suitability
Availability depends on the Mac model and macOS version. If the control is absent, do not use a copied command to force it. Review Apple's current Power Modes documentation for supported models and consider the workload: a demanding export or build may behave differently from light work.
Use comparable battery sessions to judge whether the setting fits your use. Battery percentage alone is not a measure of app efficiency, and an aging battery can affect runtime separately from a power-mode change.
Where WattGuard fits
WattGuard Full can manually change Low Power Mode for the battery or power-adapter profile with a macOS administrator prompt. This is a manual control, not a built-in battery-threshold automation action. In the Store edition, use macOS for the power mode and WattGuard for evidence around the outcome.