Battery replacement for iphone xs

I scheduled an appointment for my iphone xs battery replacement and when I reached the shop, the engineer verified my phone and mentioned its ok to go, but there is no stock. If there is no stock why apple allow me to book an appointment and waste my time. Also, I was told, I have to leave my phone for 3-4 days minimum, even if there was stock available. I think these important information should be mentioned by apple. Also another strange thing the engineer clarified that, along with the battery, the speaker also has to be changed. My iphone xs speaker is even better than my current iphone 16 pro one, then why should i change ? Overall lot of confusion by apple it seems.