Greetings DD, welcome,
The Crusader GT2 will run on 3S 11.1V or 4S 14.8V Batteries, as a beginner I would just get a couple 3S 1300mah 45C batteries. This will give you a softer and slower approach as you go through the learning curve. Then go to the 4S / 1800mah / 65C for a white knuckled...