working of a wrist watch

hi friends,
could anyone tell me the principle of working of an ordinary wrist watch. I am talking about the watch that requires a small cell(circular in shape) and that has got different needle moving within the dial..

particularly I am interested to know the role of the battery that is being engaged. There is absolutely no electrical connection within the clock; then why are we engaging the battery when we keep saying that it is a mechanical device.

please help...

regards,
proffy.