In an internal memo obtained by MacRumors, due to battery shortages for the 15-inch Retina MacBook Pro model released in 2012/2013, Apple employees are being told to replace these older laptops with newer equivalent models. All that you have to pay is the $200 battery replacement fee (or this is free if you have Apple Care).
The reasons as to why there is a battery constraint for just this particular model is unknown. It is thought that the shortages have been going on since at least March of 2017, with the shortage looking to end on the 15th of September 2017. If you have a 15-inch Retina MacBook Pro from 2012/2013 with a dodgy battery, you may want to try and get it replaced now.
There are testimonials as well from many users on reddit. User NoTNoS took his MacBook in and within 10 days had a 2017 MacBook replacement with Touch Bar for just the $200 battery replacement fee. This very useful post lays out some of the criteria needed for qualifying for a replacement.
You must have a mid-2012 or early 2013 15-inch Retina MacBook Pro and the battery must hold less than 80% max charge on 1000 charge cycles or less.
Reddit user MCWC94 had a similar experience, despite his MacBook Pro being a little beat up as well, it had a couple of dents and scratches and Apple still replaced his machine with a new 2017 model. The time where the user was waiting for the replacement, he/she was even allowed to hold onto their current machine, so you don’t have to worry about being without your laptop for a while.
Another user by the name of cpressland, managed to get a 2015 MacBook Pro, so you aren’t always guaranteed to get the newest model but it is still a nice upgrade for minimal cost.
This battery shortage is worldwide, so no matter where you are from, give it a go, you may just come out of it with a brand-new machine that is more recent for your troubles.
Update : According to a new article on MacRumors Apple now has new inventroy available to replace the defective batteries and is no longer upgrading old MacBook Pro's.