battery_pmu —
support for batteries and sensors in PCI-based Apple
  Powerbooks
The battery_pmu driver provides support for batteries
  and hardware sensors found in first generation PCI-based PowerBooks (i.e.
  Apple Powerbook 2400, 3400 and 3500 (also known as Original PowerBook G3).
  Currently it only exports a few sensors via the
  envsys(4) interface, including
  battery charge, voltage, CPU and battery temperature and AC power
  availability.
There is no APM emulation right now and the battery current sensor may return
  misleading or wrong data. This driver is considered preliminary and may be
  replaced at some point.