The Battlefield Shop (in front of the walls) spends Badges or Dragon Crystals (dc). Notable buys (badges / dc): Epic Historic General x1 = 2,040 / 6,000. Scrolls: King's Scroll Chest 360 / 1,140; Dragon Scroll Chest 1,160 / 3,420. Gems: 500 = 10/30, 1,000 = 20/60, 2,000 = 40/130, 5,000 = 110/310 (efficient badge->gem conversion). Gold: 200K = 20/50, 1M = 90/250, 1M x10 = 850/2,500. Resources: 2M = 30/90, 5M = 60/190, 20M = 260/750, 50M = 640/1,880. Monarch EXP 20,000 x20 = 680/2,000; General EXP 20,000 x20 = 340/1,000. Materials: any Lv5 = 40/130; any Lv6 = 130/380. Special Items (Gems, not badges): Battlefield Special Attack/Defense/HP Increase 9,000 gems each; Battlefield Special March Size Increase 25,000 gems. Separate Huns Invasion battlefield uses Barbarian Flags (Historic General Fragments 320/160 flags, Dragon Scroll Chest 5,500, Lv4 Skill Book Chest 3,000, Super Resource Chest 480, 100 Stamina 40, 24h Speed Up 180). For a bot, spend battlefield badges/crystals on generals and scrolls, or convert to gems/gold/resources when those are the bottleneck.
Original research source: Evony Guide Wiki