First of all, does the chemistry of the watch battery even allow it to be recharged?
I assume you're using the motor as a generator to recover energy from somewhere. What's turning this motor? You could clamp the voltage across the battery, but a better way is to disconnect the motor from the battery if the voltage gets too high.
Neither of these measures deals with the issue of the battery being charged too fast, or the particular charging algorithm that might need to be used to tell when the battery is full (just plain old battery voltage cannot be used for some battery chemistries).