Your laptop is seven years old so I would expect the battery to be failing if you have the original battery from the factory. You can check the condition of the Battery by Option-clicking on the Battery icon on the menubar (not available with Big Sur). If you are using Big Sur, then you will need to go into the "Battery" System Preferences and click on the button "Advanced" or Battery Managment(?) to actually see the battery condition (what an improvement Apple!). Any condition other than "Normal" indicates the battery is at least less than 80% of Design Capacity or the battery has a hardware issue. You can also run the Apple Diagnostics to see if any hardware issues are found, although the consumer level diagnostics don't detect all battery failures (the Apple service diagnostics are much better at detecting failures).
Your laptop is considered "Vintage" by Apple, but Apple will still repair or replace the battery as long as the necessary parts are still available. I'm not certain an Apple Store will perform repairs for products that are considered "Vintage", but an Apple Authorized Service Provider can.