My upgraded T520. Including a spare M.2 mounted on...the ultrabay, a new battery, and a quad i7 (originally a dual i5) Running a retro themed Q4OS. : r/thinkpad
SSD Upgrade for Lenovo ThinkPad T520 256GB/512GB/1TB/2TB | eBay
Upgrading the Lenovo ThinkPad T520 Display - iFixit Repair Guide