I just gifted a 2013 MBP to my father after replacing the battery. It's a pain in the neck to replace, but fairly doable if you're even slightly inclined to hardware repair and can read instructions. Worst part was dissolving all the glue. Not sure why Apple felt the need to use seemingly aviation grade VHB tape to keep the batteries in, but it's a lot of acetone and a lot of scraping to get it all off. All it took was $90 for the kit and a couple hours.