You may wait up to 5 weeks for an iPhone battery replacement.
Customers who want to replace their batteries for $29 will need to wait between 3 and 5 weeks, according to Business Insider. Apple launched in January a battery replacement program for iPhone 6 and newer, but the batteries have been in very short supplies since day one. The program became so popular, because many users decided to replace their batteries for $29 and return their iPhone to a normal fully-working state, instead of purchasing a new model.
As you probably know, iOS 10.2 and newer version had a hidden feature that intentionally throttles down your iPhone if the battery degrades to a certain state. This, according to Apple, was implemented to prevent shutdowns, but many users criticized Cupertino for not being transparent. The company promised to add a power management feature in future versions of iOS, allowing users to manually turn on/off the throttling.
Apple was expecting a short supply. In January, the company said that iPhone 6 Plus owners should wait longer for a replacement. However, the same is now happening to the other models, whose servicing schedule may vary between 3 and 5 weeks from the Store visit.