Mine is a mid-2012, the last one before the first Retina, also 2012. The battery in mine is easy to replace; I don¡¯t know about the Retina.
I¡¯ve just done a Retina Early 2015 13¡± MacBook Pro battery.
It¡¯s glued into the case, so getting it out is not so easy, but not so difficult. OWC - ?- sell a kit that includes glue dissovling liquid, the necessary 2 screwdrivers, gloves and a new battery for $84 for my computer. Took me about an hour to replace it.
Here¡¯s the page for my Early 2015 Retina MacBook Pro, and included there is a link to the instructions.
Roger
