The Difference Between Automatic and Quartz Movements
A quartz movement uses a battery to send a tiny electric current through a quartz crystal, which vibrates at a precise, constant frequency to drive the hands — accurate, low-maintenance, and inexpensive to produce.
An automatic (or "self-winding") movement instead uses a weighted rotor that swings with the natural motion of your wrist, winding the mainspring as you move through your day.
It never needs a battery, but it is more sensitive to position and temperature, which is why enthusiasts prize the small variances between one hand-built caliber and the next.