Earlier this year Apple started offering to replace the batteries of specific iPhone models free of charge. A similar opportunity is now available to owners of some MacBook Pros because a "limited number" of batteries are "expanding." They're not expanding like The Blob-expanding -- our cities are safe -- but it's still not great news for your laptop, so you'll want to get it taken care of.
This specifically applies to non-Touch Bar 13-inch MacBook Pros manufactured between October 2016 and October 2017. If you head over to Apple's support page about the issue, you'll be able to enter your serial number and see if your machine is eligible.
If so, you can bring your laptop to an authorized dealer or a retail store, or mail it to Apple's repair center, to have the battery replaced free of charge. If you've already paid yourself to have your battery replaced, contact the company and Apple might refund your expenses.