FPV racers use LiPos (lithium polymer batteries) to stay in the air. They differ in the number of cells - e.g. 3S = 3 cells - and the capacity in ampere hours - e.g. 1000 mAh.
With increasing cell count the nominal voltage of the battery increases - 3S = 11.1V, 4S = 14.8 etc. Since the nominal speed of the motors is related to the voltage of the LiPo, the thrust of the copter also increases when using LiPos with more cells.
For copters in the 180 - 250 class we recommend 3S (beginners) and 4S (advanced / professionals) lipos between 1000 mAh - 1800 mAh. When using the corresponding ESCs and motors, the use of 5S or 6S LiPos is also possible.