How to know when a watch is battery operated, or when it's a mechanical watch?

Answer 1

well, there's always the nifty idea of looking. if it has a battery, there will be a raised area on the back, about the size of a battery. if it's mechanical, you can keep it running by winding the stem!!

Answer 2

Movement of the 'seconds hand' of the battery oprated watch (if it has a 'seconds hand') is not as smooth as the winding one.

But note that this may not be valid to modern high precision watches / clocks.

Answer 3

one way to tell is to turn it over and red the back it will say on the back