It is confusing, and I’m not the best at explaining things. That’s probably why I preferred to repair jewellery and watches, and leave the selling to others - when it was possible!
When I bought my watch, it was ready to go, I paid, put it on and walked out of the shop wearing a working watch.
The battery lasted roughly from 2009 to 2019. I didn’t need to do anything to it.
I had to replace the battery back in 2019. The dealer changed and charged the new battery, changed gaskets, etc.
Once you get the battery replaced, you don’t have to do anything. Pay, get your watch back, and go.