I do apologize for the inconvenience.Please try the below steps which should be helpful for you to remove the back of the watch and also replace the battery.
- Flip over your pocket watch. Remove the back of your watch. The back of watches are either screwed on by four small Phillips head screws (unscrew them) or the watch has a press inserted back (slide a thin knife blade under the edge of the back of the watch and pry it off).
(OR)Find the small groove on the back of the watch right above the hinge,place the tip of the screwdriver (the small kind used for the screws in glasses) into the groove and gently pry off the back of the watch.
- Remove the circular watch battery out of the back of the watch.
- Take the battery to any department store or watch store and purchase a new replacement battery.
- Insert the new battery into the back of the watch.
- Screw on or push on the back of the watch. Set the watch to the correct time.
The above should be of help for you to have the battery on the pocket watch replaced and have the watch working once again.Best wishes for your effort and thank you for your time and patience.