Thanks for the reply. Is it true that if they don't have a battery replacement for the phone, they will replace with a refurbished set or something?
They won't replace with an older version of the phone right? For mine is iPhone 6s.. Would they replace with an iPhone 5 or something?
If you bother to click the link to Apple website which I shared, you can see iPhone 6S is still one of the models available for battery replacement. If no ready stock they will tell you need to wait a few days or maybe 1 week for the stock to come in.
Don’t bother getting your hopes up for replacement set or refurbished set. Such cases are rare and usually happens only under unique circumstances like the technician accidentally messed up your phone during the repair/replacement and cannot remedy. If such a case occur, they will offer you the closest available model to your current model, likely the same model, or it could be worse model (unlikely) or better model.