Apple Store will immediately replace the battery? Or they will take days to replace?

Apple will, in many cases, replace it while you wait. It should not take days.

Here's what Apple says about it:

iPhone Battery & Power - Official Apple Support

Make an appointment at an Apple Store or one of our many Apple authorized service locations, we'll try to fix your iPhone during your visit. In more complex cases, we might need to send it to an Apple Repair Center. If we do, your iPhone will be ready for pickup in 3-5 business days.

It depends on whether or not the Apple technician breaks the battery pull tabs--these are like command strips that hold a picture on a wall. Ideally the technicians pulls on the end of the battery pull tabs and it will pull out like a command strip, coming all the way out and releasing the battery. Then new battery is easily installed and the whole job can be done while you wait. But sometimes the strip will break off when pulling. In that case, Apple does not allow the technician to pry gently and grab the end of the torn strip to pull it the rest if the way out--instead they are required to tell you that "you have a complex issue" and send the device to Apple Depot where they are allowed to do that. That will take a few days.

Shan000 wrote:

Apple Store will immediately replace the battery? Or they will take days to replace?

They will replace it immediately (typically 30 minutes) unless something goes wrong. But most of the time nothing will go wrong, and you can leave with a working phone. Jessa has posted a worst case scenario, but it is rare. Apple Geniuses have a lot of experience replacing batteries and screens.

Hi

If you make an appointment for repair then it will be done same day.

Cheers

Brian 🇬-1F1E7;

In my case, they simply swapped out my old phone for a new phone and just charged me for the cost of the battery. FWIW, my phone is even older than yours -- an iPhone 5.