Source: Apple
If you want to get the new iPhone 14's battery replaced, that's going to cost a bit more than getting repairs for older iPhone models. While the battery replacement fee is $89 for older iPhones, the fee for the new iPhones will go for $129. This payment includes the cost of a new battery and service by an Apple Store or an Apple Repair Center. Replacement fees may vary if you go through a third-party Apple Authorized Service Provider.
Those who got AppleCare+ can get your iPhone 14 battery replaced for free, but the battery needs to retain 80% of its original capacity.