Powertop is a free and open source utility developed by Intel to monitor power consumption on Linux. The tool is able to display and export reports about the estimated discharge rate, and statics about processors and devices behavior. It also lets us easily tune some kernel parameters on the fly in order maximize battery life.
ACPI is the acronym for Advanced Configuration and Power Interface; as a standard, it was first implemented in the year 1996, as a successor to APM (Advanced Power Management). As a main feature, it brought the ability to handle power management at the operating system level, whereas before it was handled in BIOS. Some ACPI events on Linux are, by default, handled via systemd-logind, but more complex configurations can be achieved by installing and running the acpid service.