Thank you all for the prompt and accurate help.
The opener indeed could be opened by screw hidden under the mounting clip.
Found the battery and replaced for $2.43.
Tuned the slug until operation was restored. Hoooray!
It is always amazing how much information can be obtained from this
newsgroup. Thanks again.

One more thing, after operating a few times the door stopped functioning
even with the switch on the wall which is direct contacts.
Found the starting capacitor bad and a local motor repair shop gave me one
to try. Hoooray again!
Back in business.....
Bill