Apple have identified an issue with the batteries in non Touch Bar Macbook Pros manufactured between October 2016 and October 2017. It’s not a safety issue but can cause the battery to swell and is still significant enough for Apple to offer free replacement if your Macbook Pro was made between these dates and is one of the affected computers.
To find out whether your Macbook Pro is affected and qualifies for a free replacement check this page on the Apple website.
You’ll need to provide your Macbook Pro’s serial number. You can find it on the underside of your computer or in System Preferences - About This Mac in the Overview tab.
If you qualify for a free replacement you can take your computer to an Apple store or contact Apple to arrange shipping to a repair centre.