A 2S battery that can supply supply 30 amps or more.
The formula for batteries is mAh / 1000 x C, Example a 2200 mAh 25 C battery can supply 55 amps, 2200/1000 x 25 = 55. The amp rating is the do not exceed number, using less amps is no problem.
Is always a good idea to add a few amps for the Rx & servos.