A mobile host device configured to draw electrical energy from an energy storage
device includes a disk drive. The disk drive includes a disk drive enclosure including
a base, a spindle motor attached to the base, a disk positioned on the spindle
motor, a generator and a charging circuit. The generator may be coupled to the
disk drive enclosure and/or the mobile host device and generates electrical energy
from the motion of the mobile host device and/or disk drive. The charging circuit
is configured to charge the energy storage device using the electrical energy generated
by the generator.