I've got a mid 2012 15" unibody MBP, non retina (one of the last easily user serviceable ones).
I have used it every day since I bought it in early 13 and the battery is pretty weak now, a full charge lasts about 1.5hrs. (the 2:29 remaining shown in the screenshot seems inaccurate when you actually use the laptop)
If I click on the battery tab I get this service icon. Ideally I don't want to have to book an appointment, go to the apple store, lose use of my laptop for a day etc.
Can I purchase an official Apple battery directly from Apple and do the change my self? (I know there are lots of 3rd party batteries on Amazon / eBay, but I want a genuine part.)