The Battersea Compound consists of three free roam zones you unlock after completing Seasons 1, 2 and 3. In each of these areas you’re given various tasks to complete (the game calls them missions). There are 80 missions in total. You can check your progress at any time by pressing Start and selecting Missions.
After completing all the missions in Zone 1: Parking Lot and Zone 2: Depot, you’ll have this achievement. For a detailed guide on all missions and how to complete them, visit my solution here:Solution for Battered Battersea in DiRT 3