Apple is now replacing non-removable laptop batteries that retain less than 80% of their original charge under the AppleCare Protection Plan. The change applies to the MacBook, MacBook Air and MacBook Pro.
In a support document (https://support.apple.com/en-us/HT204054), Apple says: “Your Apple One Year Limited Warranty or AppleCare Protection Plan includes replacement coverage for a defective battery. If you purchased an AppleCare Protection Plan for your Mac notebook with a non-removable battery, Apple will replace the notebook battery at no charge if it retains less than 80 percent of its original capacity. If you don’t have coverage, you can have the battery replaced for a fee.”