I believe there's a metal contact from the circuit board of
the watch that needs to touch the back of the watch for the
beep to work. If that contact fell out when you replaced the
battery, or you bent it so it's no longer making solid
contact with the back of the watch, the beeping won't work.

I've replaced several watch batteries and there's usually
a teeny coil spring that touches the piezo on the back of the watch.
It's really easy for that spring to drop out
since it's not attached to anything.

Yes, that thin thing that looks like it's painted inside
the watch back is the piezo beeper.
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-- mejeep deMeep ferret!