The MacBook Pro 2012 can be equipped with larger SSDs and batteries
MacBook Pro (Howto): Install A Solid-State-Drive
MacBook Pro 13" Retina Display Late 2012 SSD Replacement - iFixit Repair Guide
Amazon.com: HIGHFINE 2nd 2.5'' SATA HDD SSD Hard Drive Disk DVD CD ROM Optical SuperDrive Caddy Tray Adapter for Apple Unibody MacBook/MacBook Pro 13 15 17 Early mid Late 2008 2009 2010 2011 2012.etc : Electronics
MacBook Pro 13" Retina Display Late 2012 SSD Replacement - iFixit Repair Guide
Installing MacBook Pro 15" Unibody Mid 2012 Dual Hard Drive - iFixit Repair Guide