I can't see your video (it's marked 'private') but I also inherited a ADE Optima Compact with the house I bought and I've changed the battery several times without using anything but the user code (at least the code I was given by the previous occupant to set and unset the alarm, which I assume is the 'user code'). Disclaimer - I'm not a professional alarm person.
All I did was take the cover off (the alarm sounds immediately because of the tamper switch - but you can silence it with the user code), disconnect the old battery and connect the new battery. Then replace the cover and press the 'Reset' button to get rid of the Tamper indication. Mine worked normally after doing that.