acpipmtr —
ACPI Power Meter
The acpipmtr device driver provides support for
  “power meters”. These are sensors that approximate the current
  power consumption of the system. Alternatively, a power meter may measure also
  the power gain when the system is connected to an external power supply.
The available information (namely, the power consumption) is made
    available through the
    envsys(4) API and the
    envstat(8) command.
The acpipmtr device driver appeared in
  NetBSD 6.0.
The acpipmtr driver is experimental.