AppleCare Phone/Battery Replacement

Hello. I have an iPhone 11 Pro Max I use heavily for both work and personal use (i.e. file sharing, phone calls, but also social media and graphic apps.) While I purchased this phone pre-order so I had it when it first came out it's still only about a year old. My battery health is now under 89% (which is strange considering I had an iPhone X for years and maintained 100% battery health through traade-in.) I have AppleCare+ on this phone and was wondering if/when the battery health falls below 80% will Apple provide me a new phone? I had heard they would replace the battery but does that mean I would have to be without a phone for given amount of time? I can't be as I have both my work and personal # tied to this phone. I am quite happy with this model iPhone (minus the battery) and plan to keep it until Apple unveils something "spectacular" that I can't pass up! Any info on how AppleCare+ would handle such situation would be greatly appreciated.